Free water treatment and tank calculators

Water Usage Calculator

Enter the people in the home and how you use water to estimate gallons per day, month and year, and where the water goes.

The Water Usage Calculator is a free tool that gives an estimated water usage figure for a household or small business, in gallons per day, per month and per year. Enter the people in the home, your fixtures, appliances, lawn watering and any pool top-up, and the result updates as you type. It is a quick way to estimate water usage before you check a bill, plan a supply or compare fixture types. The calculation runs in your browser, so nothing you type is uploaded, and no account or sign-up is needed. Results also show gallons and litres per person per day, cubic metres per month and per year, and a breakdown of where the water goes. You can add a water price to see the cost.
Water usage calculator example

How to use the Water Usage Calculator

  1. Start with the example household of 4, or tap a preset above the form.
  2. Enter the number of people. It must be greater than zero.
  3. Pick a Fixtures option: Standard, WaterSense or Custom. Custom lets you type your own showerhead, toilet and faucet values.
  4. Enter your indoor habits: showers per person, minutes per shower, toilet flushes, faucet minutes, and laundry and dishwasher loads per week. Replace the 20 gal laundry default with the figure for your washer.
  5. Enter the lawn area, the water applied per week and the watering weeks per year. If you have a pool, enter the monthly top-up in gal, L or m³.
  6. Optional: open More options for the less common inputs, or enter a water price per 1,000 gal to get the cost. Leave it empty to skip the cost.
  7. Read the results and any warning, then expand How it was calculated to check the formula and units.

Each quantity has its own unit menu, so metric and US units can be mixed. Reset restores the starting example. Copy result copies the result lines with a link, and Copy link copies the page address, which stores every input in the ?s= part of the URL. Print / save as PDF makes a one-page record with the inputs, results, steps and date.

How do you estimate water usage?

The calculator works by converting each use of water into a daily figure and adding the results together. Indoor uses are simple multiplications. Showers equal people × showers per day × minutes × flow in gallons per minute (gpm). Toilets equal people × flushes per day × gallons per flush. Faucets equal people × minutes per day × flow (gpm). Laundry and dishwashers equal loads per week × gallons per load ÷ 7, which turns a weekly figure into a daily one.

Outdoor use depends on area and water depth. One square foot watered with one inch of water holds about 0.6234 gallons, so the lawn formula is area × water per week × 0.6234 × watering weeks per year ÷ 365. Metric inputs are converted first, so an area in m² and the same area in ft² give the same result. Pool top-up works the same way: gallons per month × 12 ÷ 365 gives a daily average.

Flow rates decide how much water each fixture uses. Standard uses the US federal maximums: 2.5 gpm for showerheads, 1.6 gallons per flush for toilets and 2.2 gpm for faucets. WaterSense uses the EPA label values of 2.0 gpm, 1.28 gallons per flush and 1.5 gpm for bathroom faucets. In the worked example, the same household drops from 267.9 gal/day to 223.1 gal/day, a saving of about 44.8 gal/day, when switched to WaterSense fixtures.

Per-person figures divide the daily total by the number of people. Monthly values use 365 ÷ 12 days, and litre figures use 1 US gal = 3.785411784 L.

How accurate is the estimate?

The result is only as good as the habits you enter. Replace default assumptions with your own measured values where you can, such as your washer’s gallons per load. If a warning appears, check your units and lawn area before using the number.

Sources

Checked October 2026:

  • EPA WaterSense, statistics and facts: 82 gallons per person per day at home (USGS 2015 data)
  • EPA WaterSense, showerheads: WaterSense showerheads use no more than 2.0 gpm; standard showerheads 2.5 gpm
  • Federal maximums for toilets (1.6 gpf) and faucets (2.2 gpm at 60 psi), and the 5 gallon per cycle limit for standard dishwashers (US DOE, 10 CFR 430.32)

For estimation; verify critical designs against the applicable standard.

Worked examples

InputResult
household of 4, standard fixtures, lawn 2000 ft²267.9 gal/day, 8,147 gal/month, 67 gal per person per day
household of 4, WaterSense fixtures, lawn 2000 ft²223.1 gal/day, 6,785 gal/month, 55.8 gal per person per day
household of 2, standard fixtures101.9 gal/day, 3,100 gal/month, 51 gal per person per day
household of 4, custom flow rates, lawn 2000 ft²203.5 gal/day, 6,189 gal/month, 50.9 gal per person per day
household of 1, standard fixtures, lawn 100 m²135.4 gal/day, 4,117 gal/month, 135 gal per person per day

Calculated by the tool above with these values.

Frequently asked questions

Can I use the results in commercial projects or client reports?

Yes. You may use the results in commercial work, including quotes, reports and client projects, without attribution. They are estimates, so treat them as such in critical designs.

Is the calculator free, and is anything I type uploaded?

Yes, it is free. Everything is calculated in your browser, nothing you type is uploaded, and there is no account or sign-up.

Can I print or share a calculation?

Yes. Print / save as PDF gives you a one-page record with the inputs, results, calculation steps and date. To share a calculation, use Copy link and send the address to someone, and they will see the same inputs.

What should I enter for the laundry load size?

Enter the gallons per load for your own washer, which is usually listed in the manufacturer’s specifications. The default of 20 gal per load is only a starting figure. Laundry use scales directly with this value, so the change shows up in the breakdown table.

Why does the calculator show a warning?

Warnings appear for more than 2 hours of showering per person per day, unusually high custom flow rates, and more than 500 gal per person per day. The last one usually points to a unit or lawn-area mistake, so check those inputs first.

What does an error message mean?

An error stops the result until you fix the input. The number of people must be greater than zero, values cannot be negative, watering weeks cannot exceed 52, and at least one use must be above zero.

Can I enter my data in metric units?

Yes. Each quantity has its own unit menu, so you can mix metric and US customary units in one calculation. Lawn area can be in ft² or m², and pool top-up can be in gal, L or m³.

Does the cost include sewer charges?

Not automatically. The price is per 1,000 gal, and it gives the monthly and yearly cost. If your sewer charges are billed by use, add them into the price.