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Cost per flush and toilet payback.

Cost per flush is gallons per flush x your price per gallon; a 1.28 gallon WaterSense toilet uses 20 percent less than the 1.6 gallon federal standard, and older toilets use far more. Enter your old and new flush volumes and your use to see cost per flush, gallons saved and years to pay back. Runs in your browser; nothing is sent or stored.

Your numbers

Old toilet (gallons per flush)

Marked on the tank or bowl. The EPA says older toilets can use as much as 6 gallons per flush. 3.5 is an example.

New toilet (gallons per flush)

EPA: WaterSense toilets use 1.28 gpf or less; the federal standard is 1.6.

Flushes per person per day

Your household's habit; 5 is an example.

People in the household

Water price (include sewer if billed per volume)

Example value. Use the rate on your own bill.

Water price is per

Price of the new toilet, installed

Example value.

Rebate (optional)

Example value; check your utility.

Result

Fill the form and press Calculate.

Worked example

Four people flushing 5 times a day make 7,300 flushes a year. An old 3.5 gallon toilet uses 25,550 gallons; a 1.28 gallon toilet uses 9,344, so you save 16,206 gallons (63% less). At an example $10 per 1,000 gallons, a flush costs 3.50 cents on the old toilet and 1.28 cents on the new one, a yearly saving of $162.06. A $250 toilet with a $50 rebate costs $200 net and pays back in about 1.2 years. Example inputs: replace them with your own.

How it works

Cost per flush = gallons per flush / 1,000 x price per 1,000 gallons. Yearly gallons = gallons per flush x flushes per person per day x people x 365. Saving = (old - new) x flushes x price. Payback = (price - rebate) / yearly saving. The EPA says older toilets can use as much as 6 gallons per flush, that the current federal standard is 1.6 gallons per flush, and that WaterSense labelled toilets use 1.28 or less.

Not covered. Dual-flush toilets use different volumes for liquids and solids; enter an average. Include sewer charges in the price if your utility bills them by volume. A leaking toilet wastes more than its flushes, so run the dye test too.

Sources and basis (pages opened 2026-10-08): US EPA WaterSense, Residential Toilets; US EPA WaterSense, Fix a Leak Week.

This is a planning estimate and not professional plumbing, electrical or financial advice. Rates, fixtures and equipment vary, so confirm important decisions with your utility, the manufacturer or a licensed professional.

FAQ

How much water does a toilet use per flush?

The EPA says the current US federal standard is 1.6 gallons per flush, WaterSense labelled toilets use 1.28 or less, and older toilets can use as much as 6 gallons per flush.

How much does one flush cost?

Gallons per flush divided by 1,000, multiplied by your price per 1,000 gallons. At an example $10 per 1,000 gallons, a 1.28 gallon flush costs about 1.3 cents.

How much can a new toilet save?

The EPA says replacing old toilets with WaterSense models reduces toilet water use by 20 to 60 percent. Your own saving depends on your old toilet and your use.

How do I find my toilet's gallons per flush?

Look for the marking on the tank, the bowl rim or under the lid. Toilets made before the 1.6 gallon standard use more.

Should I check for a leak first?

Yes. A leaking flapper can waste more than the flushes themselves; do the food colouring dye test before spending money.