A complete breakdown of water consumption, flush performance, MaP test scores, EPA WaterSense certification, and real-world clog resistance -- so you can buy the right toilet with confidence.
Research updated June 2026.
A 1.28 GPF toilet saves roughly 4,000 gallons per household per year versus a 1.6 GPF model and earns EPA WaterSense certification. Modern 1.28 GPF toilets -- including the TOTO Drake II and American Standard Cadet 3 -- match or exceed the flush power of older 1.6 GPF designs, making them the better choice for most households.
When you stand in a plumbing showroom comparing toilet spec sheets, two numbers appear constantly: 1.28 gallons per flush (GPF) and 1.6 GPF. Those 0.32 gallons sound trivial. Across a family of four over a year, they translate to roughly 4,000 to 7,000 gallons -- enough to fill a small backyard pool. More importantly, the gap in flush performance between the two standards has nearly closed thanks to a decade of engineering improvements in bowl geometry, trapway diameter, and jet design.
This guide cuts through the marketing language to explain what each standard actually means, how third-party MaP flush testing measures real performance, which specific toilet models perform best at each GPF rating, and whether spending more on a high-efficiency model pays off in water bill savings. Internal links throughout connect to deeper dives on related topics covered in our best flushing toilets roundup.
GPF stands for gallons per flush -- the volume of water a toilet uses in a single flush cycle. The 1.6 GPF standard became federal law in the United States under the Energy Policy Act of 1992, replacing older 3.5 GPF and 5 GPF models. The 1.28 GPF standard is the threshold for EPA WaterSense certification, introduced in 2006, and requires that a toilet use no more than 1.28 gallons while still achieving a minimum MaP score of 350 grams. Both standards are legal for new construction, but only 1.28 GPF models qualify for WaterSense labeling and many local utility rebates.
The practical difference comes down to water volume and the engineering required to move waste reliably with less water. A 1.6 GPF toilet relies on volume -- more water rushing through the bowl creates momentum to clear the trapway. A 1.28 GPF toilet must compensate with bowl shape, trapway design, and jet or siphon mechanics engineered to generate equivalent or superior hydraulic force using less water.
Early high-efficiency toilets (HETs) from the late 2000s struggled with this trade-off. First-generation 1.28 GPF models sometimes required two flushes to clear solid waste, effectively defeating the water savings. Today, the engineering has caught up. Independent MaP testing routinely records 1.28 GPF toilets scoring 800 to 1,000 grams -- the maximum rating -- which is identical to or better than many 1.6 GPF models on the market.
| Feature | 1.28 GPF (HET) | 1.6 GPF (Standard) |
|---|---|---|
| Water per flush | 1.28 gallons | 1.6 gallons |
| EPA WaterSense eligible | Yes | No |
| Annual water use (4 flushes/day/person, 4 people) | ~7,475 gallons | ~9,344 gallons |
| Water saved per year vs. 1.6 GPF | ~1,869 gallons/household | Baseline |
| Max MaP score achievable | 1,000 g (top models) | 1,000 g (top models) |
| Utility rebate eligibility | Most programs | Rarely |
| Federal legal standard (post-1994) | Yes (also meets 1.6) | Yes |
| Typical price range | $150 - $800+ | $100 - $600+ |
| Available in dual-flush | Yes (0.8/1.28 GPF common) | Yes (1.0/1.6 GPF) |
Yes, in most cases. The MaP (Maximum Performance) flush testing protocol -- which measures how many grams of solid waste a toilet can reliably clear in a single flush -- shows that top-rated 1.28 GPF toilets perform at the same 800 to 1,000 gram level as the best 1.6 GPF models. The TOTO Drake II (1.28 GPF) scores 1,000 grams on MaP tests, as does the American Standard Champion 4 (1.6 GPF) -- demonstrating that flush power is primarily a function of trapway engineering and bowl geometry, not raw water volume.
MaP testing is the standard buyers and plumbers rely on because it measures actual performance rather than manufacturer claims. The protocol was developed jointly by the Alliance for Water Efficiency, the Canadian Water and Wastewater Association, and various water utility partners. Toilets are tested in a certified lab using soybean paste mixed to simulate real-world waste density. A score of 350 grams is the minimum for EPA WaterSense certification; premium toilets routinely reach 800 to 1,000 grams regardless of GPF rating.
A toilet's MaP score is a far better predictor of real-world flush performance than GPF alone. A 1.6 GPF toilet with a small trapway and poor bowl design will clog more often than a well-engineered 1.28 GPF model with a fully glazed 2-3/8 inch trapway. When comparing models, check MaP scores first, then GPF as a secondary water-cost factor.
The key engineering factors that allow 1.28 GPF toilets to flush powerfully with less water include:
Switching from a 1.6 GPF toilet to a 1.28 GPF model saves approximately 1,869 gallons per toilet per year based on the EPA's estimate of 4 flushes per person per day for a family of four. At a national average water rate of $0.006 per gallon (including sewer charges), that represents roughly $11 to $22 in annual savings per toilet -- but households replacing pre-1994 toilets (3.5 to 5 GPF) can save 13,000 to 20,000 gallons per year and qualify for utility rebates that frequently offset 20 to 50 percent of purchase cost.
The EPA estimates that toilets account for about 30 percent of indoor household water use, making them the single largest indoor water consumer. Nationally, WaterSense-labeled toilets have collectively saved more than 580 billion gallons of water since the program launched in 2006, according to EPA program data.
Water cost savings vary significantly by geography. In drought-prone states like California, Arizona, and Colorado, municipal water rates are often two to four times the national average, and utility rebates for WaterSense toilets can reach $100 to $250 per unit. In these markets, the payback period for choosing a 1.28 GPF over a 1.6 GPF model can be as short as one to three years. In lower-cost water markets, the financial case is more modest, though the environmental benefit remains the same.
| Scenario | 1.28 GPF Annual Use | 1.6 GPF Annual Use | Annual Savings |
|---|---|---|---|
| One toilet, household of 4 | 7,475 gal | 9,344 gal | 1,869 gal |
| Two toilets, household of 4 | 14,950 gal | 18,688 gal | 3,738 gal |
| Replacing 3.5 GPF (pre-1994) with 1.28 GPF | 7,475 gal | 20,440 gal | 12,965 gal |
For households still using pre-1994 toilets using 3.5 to 5 GPF, the savings from upgrading to a 1.28 GPF model are dramatic. The EPA's WaterSense program estimates that replacing one pre-1994 toilet with a WaterSense-certified 1.28 GPF model saves more than 13,000 gallons per year -- and that many utility rebate programs prioritize these replacement scenarios with the highest rebate amounts.
Most major toilet manufacturers now produce their flagship lines in both 1.28 GPF and 1.6 GPF configurations. TOTO's Drake and Drake II lines offer 1.28 GPF versions with MaP scores of 800 to 1,000 grams; the TOTO UltraMax II is a 1.28 GPF one-piece at 1,000 grams. Kohler's Cimarron and Highline are available in both ratings; the Kohler Highline Classic remains popular at 1.6 GPF for its proven reliability. American Standard's Cadet 3 is offered at both ratings, while the Champion 4 at 1.6 GPF holds a MaP score of 1,000 grams.
TOTO Drake II (1.28 GPF, Two-Piece) -- The Drake II uses TOTO's double cyclone flush system with two nozzles rather than a traditional rim wash to generate a powerful 1,000-gram MaP flush. The fully glazed 2-3/8 inch trapway and CEFIONTECT ion-barrier glaze reduce buildup. It is WaterSense certified and widely available. See our detailed TOTO Drake vs Drake II comparison for specifications across both generations.
TOTO UltraMax II (1.28 GPF, One-Piece) -- TOTO's one-piece flagship also scores 1,000 grams on MaP testing. The skirted design simplifies cleaning while the Universal Height (17.25 inches) suits most adults. CEFIONTECT glaze is standard on most configurations.
American Standard Cadet 3 (1.28 GPF) -- One of the most reviewed toilets in the mid-range segment, the Cadet 3 at 1.28 GPF scores consistently high on MaP testing (800 to 1,000 grams depending on configuration). The PowerWash rim scrubs the bowl with each flush and the fully-glazed trapway is 2-3/8 inches. Learn more in our American Standard Cadet 3 review.
Woodbridge T-0001 (1.28 GPF, One-Piece) -- The Woodbridge T-0001 is a popular value-oriented one-piece with a soft-close seat included and WaterSense certification. Owner reviews consistently note adequate flush performance for everyday use, though MaP scores are not publicly listed by the manufacturer.
Gerber Avalanche (1.28 GPF) -- Gerber's Avalanche line uses a 3-inch flush valve -- larger than the industry standard 2-inch -- to deliver a high-volume, fast flush at 1.28 GPF. MaP testing records 1,000-gram performance on select configurations.
Swiss Madison Sublime II (1.28 GPF) -- The Swiss Madison Sublime II is a rimless, wall-faced one-piece that uses a fully skirted design. WaterSense certified; owner reviews note strong flush performance for a value-priced one-piece.
American Standard Champion 4 (1.6 GPF) -- The Champion 4 remains one of the most clog-resistant 1.6 GPF toilets on the market, with a 4-inch accelerator flush valve and a 2-3/8 inch fully glazed trapway that produces a 1,000-gram MaP score. American Standard markets it specifically as a large-trapway, high-clearance design. Our full American Standard Champion 4 review covers performance and long-term owner satisfaction.
Kohler Highline Classic (1.6 GPF) -- A stalwart in the Kohler lineup, the Highline Classic at 1.6 GPF is widely used in rental properties and new construction. It uses Kohler's Class Five flush technology with a 3-1/4 inch by 2-1/8 inch trapway. MaP scores range from 800 to 1,000 grams depending on configuration.
Kohler Cimarron (1.28 GPF and 1.6 GPF) -- Kohler offers the Cimarron in both ratings, making it a useful direct comparison point. Owner reviews and aggregated feedback suggest the 1.28 GPF Cimarron performs nearly identically to the 1.6 GPF version in everyday use, consistent with MaP test results.
If a household is torn between the two standards, a useful rule of thumb is to check whether the specific 1.28 GPF model has a published MaP score of at least 600 grams. Models at or above that threshold handle real-world waste loads reliably. Below 500 grams, double-flushing becomes a realistic concern -- negating both the water savings and the convenience advantage.
Yes on both counts. EPA WaterSense certification, which requires 1.28 GPF or less, guarantees third-party verification that the toilet uses at least 20 percent less water than the federal 1.6 GPF standard while meeting a minimum 350-gram MaP flush performance threshold. WaterSense-labeled toilets are eligible for rebates from more than 1,000 U.S. water utilities and municipal programs, with rebate amounts typically ranging from $25 to $250 per toilet. The 1.6 GPF standard meets federal law but does not qualify for WaterSense labeling or the majority of rebate programs.
The EPA WaterSense program provides a searchable rebate finder on its website (epa.gov/watersense) where homeowners can locate utility rebates by ZIP code. In many California and Arizona municipalities, rebates stack with state-level water conservation incentives, further reducing net purchase cost. Some jurisdictions -- including parts of California -- mandate WaterSense-level efficiency for new construction and renovation, effectively making 1.28 GPF or lower the only compliant option.
For environmental impact, the water efficiency advantage of a 1.28 GPF toilet compounds over its 10 to 25 year service life. A household of four replacing two 1.6 GPF toilets with 1.28 GPF WaterSense models conserves approximately 75,000 gallons over 20 years -- per toilet -- which represents meaningful stress relief for municipal water treatment infrastructure, especially in water-scarce regions.
In a small number of situations, a 1.6 GPF toilet may be worth considering. Older plumbing with low-slope drain lines (less than 1/4 inch drop per foot) can struggle to carry solids to the main sewer line with only 1.28 gallons of flush water, and a higher-volume flush can compensate for inadequate drain slope. Additionally, households with very high solid waste loads -- commercial settings, large families with young children -- may find the extra water volume provides a practical margin in older drain configurations.
However, these situations are less common than they once were. Most residential plumbing installed after 1990 has adequate drain slope for 1.28 GPF performance, and most modern 1.28 GPF toilets have trapways large enough to pass waste without relying on volume alone. If you are uncertain about your drain configuration, a licensed plumber can assess drain slope before a toilet purchase.
A second scenario where 1.6 GPF remains relevant is replacement parts availability. In commercial settings, rental units, or older buildings where standardization matters, a 1.6 GPF Kohler or American Standard tank may already be the resident model and replacing with an identical unit simplifies parts sourcing. This is a logistical argument, not a performance one.
For new bathroom construction or a full bathroom remodel, there is almost no engineering reason to choose 1.6 GPF over a well-rated 1.28 GPF toilet. The water savings, rebate eligibility, and WaterSense certification are all advantages on the 1.28 GPF side. The only compelling case for 1.6 GPF is maintaining consistency in a building where a specific 1.6 GPF model is already standardized for parts and serviceability.
Dual-flush toilets offer a third path, combining a reduced-volume flush (typically 0.8 to 1.0 GPF) for liquid waste with a full flush (1.28 or 1.6 GPF) for solid waste. The TOTO Aquia IV, for example, is a dual-flush model rated 0.8/1.28 GPF and earns WaterSense certification. When used as designed -- partial flush for liquids, full flush for solids -- a dual-flush toilet can reduce average water consumption below 1.0 GPF per flush for many households.
Owner reviews of dual-flush models note a learning curve in the first weeks of use, but long-term satisfaction is generally high. For households focused on maximum water conservation, a dual-flush model like the TOTO Aquia IV or the Woodbridge T-0001 in dual-flush configuration represents the lowest water consumption option while maintaining reliable solid waste clearance. Read more about this option in our guide on how dual flush toilets work.
Homes with water pressure below 25 psi can sometimes experience reduced flush effectiveness in any gravity-feed toilet, including 1.28 GPF models. In low-pressure scenarios, pressure-assist toilets -- which use compressed air in the tank to boost flush force -- are available in both 1.28 GPF and 1.6 GPF configurations. Pressure-assist 1.28 GPF models from American Standard and Gerber score near the maximum on MaP testing even at lower inlet pressures, at the cost of louder flush noise.
For most homeowners replacing an existing toilet or specifying one for new construction, a WaterSense-certified 1.28 GPF toilet with a MaP score of 600 grams or higher is the right choice in 2026. It saves water, qualifies for rebates, meets or exceeds the flush performance of most 1.6 GPF models, and is available across every price point from value-oriented brands like Woodbridge and Swiss Madison to premium engineered lines like TOTO and Kohler. The 1.6 GPF standard still meets federal law and suits specific replacement scenarios, but it no longer represents the performance ceiling it once did. A well-chosen 1.28 GPF toilet is better by nearly every measure that matters.
GPF stands for gallons per flush. It measures the volume of water a toilet tank releases during a single flush cycle. Lower GPF means less water used per flush.
Yes, when the toilet has a well-engineered trapway and flush system. Many 1.28 GPF toilets earn MaP scores of 800 to 1,000 grams -- the highest rating -- meaning they reliably clear heavy solid waste loads in a single flush.
MaP (Maximum Performance) is an independent third-party testing protocol that measures how many grams of simulated solid waste a toilet can clear in a single flush. Scores range from 0 to 1,000 grams. A score of 350 grams is the minimum for EPA WaterSense certification; 600 grams or above is considered strong performance.
Yes. WaterSense requires toilets to use no more than 1.28 GPF and achieve a minimum MaP score of 350 grams. All WaterSense-labeled toilets are third-party verified to meet both criteria.
In most U.S. markets, yes. Over 1,000 water utilities and municipal programs offer rebates for WaterSense-certified 1.28 GPF toilets. Rebate amounts typically range from $25 to $250. Use the EPA's WaterSense rebate finder at epa.gov/watersense to check programs in your ZIP code.
Both versions exist. TOTO sells the Drake in 1.28 GPF and 1.6 GPF configurations. The 1.28 GPF version is WaterSense certified; the 1.6 GPF version provides slightly more water volume per flush. The Drake II is primarily offered in the 1.28 GPF configuration with TOTO's double cyclone flush technology.
Based on the EPA estimate of 4 flushes per person per day, a family of four using one 1.28 GPF toilet flushes approximately 7,475 gallons per year. Two toilets in the same household would use approximately 14,950 gallons per year from toilet flushing alone.
A standard 1.28 GPF toilet uses the same water volume for every flush. A dual-flush toilet offers two options: a partial flush (typically 0.8 to 1.0 GPF) for liquid waste and a full flush (1.28 or 1.6 GPF) for solid waste, reducing average water use when partial flushes are used consistently for liquids.
Not necessarily. Flush performance depends far more on trapway size, bowl design, flush valve diameter, and engineering than on raw water volume. Many 1.28 GPF toilets outperform 1.6 GPF models on MaP testing. Volume-based advantages of 1.6 GPF are most relevant in low-pressure systems or plumbing with inadequate drain slope.
A fully glazed trapway of at least 2-1/8 inches is considered the minimum for reliable performance at 1.28 GPF. Premium models from TOTO and American Standard feature 2-3/8 inch fully glazed trapways, which provide additional margin for clog resistance. Fully glazed means the interior of the trapway is coated to reduce waste adhesion and buildup.
No. The American Standard Champion 4 uses 1.6 GPF. It is a high-volume model specifically designed with a 4-inch accelerator flush valve for maximum clog resistance. American Standard's Cadet 3 line is available in a 1.28 GPF WaterSense-certified configuration.
Yes. The federal standard requires toilets to use no more than 1.6 GPF; 1.28 GPF is below that threshold and legal everywhere. Some states -- including California, Texas, and Colorado -- have stricter requirements mandating 1.28 GPF or lower for new construction, effectively requiring HET models.
Toilet height (the distance from floor to seat) does not directly affect flush performance. Comfort Height or ADA-compliant toilets (typically 16 to 18 inches) and Standard Height toilets (14 to 15 inches) can both achieve equivalent MaP scores at 1.28 GPF. Height choice is primarily a comfort and accessibility consideration.
The TOTO Aquia IV is a dual-flush toilet rated 0.8 GPF for the partial flush and 1.28 GPF for the full flush. Both flush modes are WaterSense compliant. The Aquia IV is one of TOTO's most efficient models, representing the lower end of the 1.28 GPF category when used on the full-flush setting.
MaP scores are published at map-testing.com, which maintains a searchable database of tested toilet models. You can search by manufacturer, model name, or model number to find the recorded MaP score and the GPF rating under which it was tested.
In most cases, yes. Standard residential plumbing designed for 1.6 GPF toilets is compatible with 1.28 GPF models. The main variable is drain slope: a minimum of 1/4 inch drop per linear foot of drain pipe is recommended. If your home has adequate drain slope for a 1.6 GPF toilet, a 1.28 GPF model should work without plumbing modifications.
Yes. Kohler offers many of its most popular lines -- including the Cimarron, Santa Rosa, and Wellworth -- in 1.28 GPF WaterSense-certified configurations. The Kohler Highline is available in both 1.28 GPF and 1.6 GPF versions, making it a direct comparison benchmark between the two standards within the same product family.
Yes. Gerber's Avalanche and Viper lines include WaterSense-certified 1.28 GPF models. Gerber's 3-inch flush valve -- larger than the 2-inch industry standard -- provides strong flush performance at reduced water volume, and select Gerber 1.28 GPF models record 1,000-gram MaP scores.
Prior to the Energy Policy Act of 1992, toilets commonly used 3.5 to 5 GPF, with some older models using up to 7 GPF. The 1.6 GPF federal standard took effect for new toilets in 1994. The EPA WaterSense 1.28 GPF standard launched in 2006 as a voluntary certification program above and beyond the federal minimum.
Yes. Pressure-assist toilets use compressed air in a sealed tank to augment flush force and are available in 1.28 GPF configurations from American Standard and Gerber. They are particularly useful in low-pressure water supply situations or for homes with long horizontal drain runs where gravity alone may not provide sufficient flush momentum.
How we rank & our data sources
We do not run physical lab tests. Rankings are built from published, verifiable data and real owner feedback, never paid placement.
Researched by Marcus Bell · Last updated August 14, 2026 · Our review method
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