What Toilet Should I Buy?

How to Choose a Toilet: The Complete Buyer's Guide

Buying a toilet is one of the more permanent fixture decisions in a home — most toilets last 25–50 years with proper maintenance, and the wrong choice means living with it through countless daily interactions. The key metrics that actually determine toilet quality are MaP performance score, gallons per flush (GPF), rough-in measurement, bowl height, and flushing technology. Understanding these specifications before shopping saves money, avoids costly installation mistakes, and ensures you get a toilet that performs reliably for decades.

MaP Testing: The Only Real Measure of Flush Performance

MaP (Maximum Performance) is an independent flush-performance testing protocol developed by the Canadian Water and Wastewater Association and administered by Veritec Consulting and Koeller & Company. Toilets are tested using a soybean paste media that has been engineered to simulate real-world waste in terms of density and cohesion. The test progressively increases the mass of media until the toilet fails to clear in a single flush, establishing a maximum performance rating in grams.

The rating scale breaks down as follows:

The critical insight from MaP testing is that GPF and flush performance are independent variables. A poorly designed 1.6 GPF toilet can score 350g, while a well-engineered 1.0 GPF model can score 1,000g. The key is the size and geometry of the trapway, the flush valve opening diameter, and the engineering of the rim jets or tornado channels that direct water flow through the bowl. Always look at MaP score first, GPF second.

Siphonic vs. Washdown: The Two Flush Systems

US toilets almost universally use a siphonic flush system: water enters the bowl rapidly, creates a siphon action in the trapway, and the resulting negative pressure pulls waste down and out. Siphonic toilets have a longer, more tortuous trapway that curves up before descending — this water seal prevents sewer gases from entering the home without needing a separate trap.

European washdown toilets use a simpler, more direct flush: water rushes from the tank into the bowl and physically pushes waste down through a short, steep trapway. Washdown toilets are louder (no siphon dampening), have a more visible water surface area in the bowl (the water shelf), and require more frequent bowl cleaning due to waste deposits above the water line. They are simpler mechanically and rarely clog. In the US, washdown toilets are almost exclusively found in wall-hung configurations.

Rough-In: Measure Before You Buy

The rough-in distance is the measurement from the finished wall surface (not the baseboard trim) to the center of the drain flange — the same point that aligns with the center of the floor bolts (closet bolts) at the base of the toilet. Standard rough-ins in the United States are:

• 10 inches: Found in older homes, small bathrooms, and some condos where plumbing was run close to the wall. Requires a specifically designed 10" rough-in toilet — they have a shallower tank depth.
• 12 inches: The overwhelming standard for US homes built after 1960. The vast majority of toilets on the market are designed for 12" rough-in.
• 14 inches: Found in some pre-1940 homes and in bathrooms that were later modified. Requires a 14" rough-in toilet or a 12" model with an offset flange adapter.

Installing a toilet with the wrong rough-in is not correctable through shimming or adjustments. A 12" toilet in a 10" rough-in space leaves a visible 2-inch gap between the back of the tank and the wall — unattractive and a leverage point for rocking. Measure before purchasing without exception.

Two-Piece vs. One-Piece: What the Difference Actually Means

Two-piece toilets have a separate tank and bowl that bolt together during installation. They dominate the market because they ship in smaller boxes (tank and bowl separately), are easier to carry up stairs, and are cheaper to repair — a cracked tank can be replaced without buying a new bowl. The bolted tank-to-bowl connection uses a rubber gasket that can degrade over time, potentially causing a slow leak at the base of the tank. This is the principal maintenance point of a two-piece toilet and is cheap to fix.

One-piece toilets are cast as a single unit. There is no tank-to-bowl joint, so there is no gasket to fail there. The surface is continuous and much easier to clean — no seam in the rear lower area of the tank where mold and mineral deposits accumulate in two-piece models. One-piece toilets are heavier (often 90–120 lbs vs 50–70 lbs for a two-piece), more expensive to ship, and typically command a 20–40% price premium for equivalent performance. They are the dominant choice in high-end residential bathrooms.

Standard Height vs. ADA Comfort Height

Standard toilets have a rim height of 14–15 inches. ADA comfort height toilets have a rim height of 16–18 inches. The ADA standard for accessible bathrooms requires a toilet seat height of 17–19 inches when the seat is installed. For residential use, the choice depends on the primary users.

Taller adults (generally 5'9" and above) typically find comfort height more ergonomic — the hip angle is closer to a standard chair height, reducing knee and hip strain over extended use. Shorter adults and children find standard height easier to sit down onto and stand up from. In households with mixed users, comfort height is generally the better default since it can always be supplemented with a step stool for children but cannot be lowered for short users.

Flush Technology Comparison: TOTO, Kohler, and American Standard

The three major US toilet brands each use proprietary flushing technologies that approach bowl clearing differently:

• TOTO Tornado Flush: Uses two nozzles set at angles that create a centrifugal, cyclonic water action around the bowl — similar to a vortex. This replaces traditional rim holes entirely, eliminating the under-rim mineral buildup that plagues older designs. TOTO's Tornado Flush is widely regarded as the most thorough bowl-cleaning flush in the residential market.
• Kohler AquaPiston: A canister-style flush valve that opens 360 degrees (vs. a traditional flapper that lifts from one side). This allows 90% more water to flow into the bowl at the start of the flush, creating a stronger initial surge. AquaPiston is compatible with both gravity and pressure-assist tanks.
• American Standard VorMax: Uses an angled jet at the top of the bowl that creates a turbulent vortex action, combined with an elongated channel that concentrates the water flow. American Standard claims VorMax cleans 2x more of the bowl per flush versus their previous design.

GPF Guide: What the Numbers Mean for Your Water Bill

The federal flush volume timeline establishes clear benchmarks: the Energy Policy Act of 1992 mandated a maximum of 1.6 GPF for all toilets sold in the US after January 1, 1994. The EPA's WaterSense program (2006) established a 1.28 GPF voluntary certification threshold with a minimum MaP score of 350g. High-efficiency toilets (HET) are generally defined as 1.1 GPF or below, and ultra-high-efficiency (UHET) toilets reach 0.8 GPF.

A common misconception is that very low GPF toilets necessarily perform worse. This is not true when the MaP score is high. A 1.28 GPF WaterSense toilet with a 1,000g MaP score will flush more reliably than a 1.6 GPF toilet with a 500g MaP score, while using 20% less water. The savings for a 4-person household switching from 3.5 GPF (pre-1994) to 1.28 GPF amount to approximately 29,000 gallons per year — enough to fill a standard backyard swimming pool.