Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Monthly usage (gallons)
5,312
Estimated monthly bill
$34.53
Daily usage (gallons)
177
Per person per day
44.3
Annual usage (gallons)
64,626
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter people in household.
- 2Enter shower minutes per person per day.
- 3Enter showerhead flow (gpm).
- 4Enter toilet flushes per person per day.
- 5Enter gallons per flush.
- 6Enter laundry loads per week.
- 7Enter water rate ($/1000 gal).
- 8Read your monthly usage (gallons) on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Showers, toilets, laundry, and irrigation account for most household water. Swapping to a 1.5 gpm showerhead saves more than almost any other single change.
Worked example
Using the values the calculator loads with:
Inputs
- People in household: 4
- Shower minutes per person per day: 8
- Showerhead flow: 2.1 gpm
- Toilet flushes per person per day: 5
- Gallons per flush: 1.6
- Laundry loads per week: 5
- Water rate: 6.5 $/1000 gal
Results
- Monthly usage (gallons): 5,311.71
- Estimated monthly bill: $34.53
- Daily usage (gallons): 177.06
- Per person per day: 44.3
- Annual usage (gallons): 64,625.86
What each field means
Inputs
- People in household
- The people in household used in the calculation. Starts at 4 so you have a working example on load.
- Shower minutes per person per day
- The shower minutes per person per day used in the calculation. Starts at 8 so you have a working example on load.
- Showerhead flow (gpm)
- The showerhead flow used in the calculation, measured in gpm. Starts at 2.1 gpm so you have a working example on load.
- Toilet flushes per person per day
- The toilet flushes per person per day used in the calculation. Starts at 5 so you have a working example on load.
- Gallons per flush
- The gallons per flush used in the calculation. Starts at 1.6 so you have a working example on load.
- Laundry loads per week
- The laundry loads per week used in the calculation. Starts at 5 so you have a working example on load.
- Water rate ($/1000 gal)
- The water rate used in the calculation, measured in $/1000 gal. Starts at 6.5 $/1000 gal so you have a working example on load.
Results
- Monthly usage (gallons)
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated monthly bill
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Daily usage (gallons)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Per person per day
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Annual usage (gallons)
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the water usage calculator work?
Showers, toilets, laundry, and irrigation account for most household water. Swapping to a 1.5 gpm showerhead saves more than almost any other single change. The underlying maths is: Gallons = Sum of each fixture's flow × frequency × household size.
What do I need to enter?
7 values: people in household, shower minutes per person per day, showerhead flow, toilet flushes per person per day, gallons per flush, laundry loads per week, and water rate. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the monthly usage (gallons) result mean?
It is returned as a whole number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Water Usage Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/water-usage
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/water-usage" target="_blank" rel="noopener">Water Usage Calculator — RevenueLab</a> (2026).</p>
Source: [Water Usage Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/water-usage) (2026).