Water Usage Calculator

How to use the calculator

Enter the number of people, then each habit and the matching flow rate or gallons per use. Laundry, dishwasher and outdoor use are per week for the whole household; faucet minutes are per day for the whole household. Enter your water price per 1,000 gallons from your bill.

What the result means

Three people with 8-minute 2 gpm showers and the other example habits use about 125.36 gal/day, or roughly 3,816 gallons a month, $22.89 at an example $6 per 1,000 gallons. Showers are the largest share at about 38%.

Formula and units

Showers = people × showers per person × minutes × flow rate; toilets = people × flushes × gallons per flush; laundry and dishwasher = loads per week × gallons per load ÷ 7; faucets = minutes per day × flow rate; outdoor = gallons per week ÷ 7. Daily use is the sum. Monthly = daily × 30.4375 (365.25 ÷ 12); annual = daily × 365.25. Cost = gallons ÷ 1,000 × your price per 1,000 gallons.

Worked examples

Three people with weekly outdoor watering: People in the household: 3 people; Showers per person per day: 1 showers; Minutes per shower: 8 min; Shower flow rate (label or measured): 2 gal/min; Toilet flushes per person per day: 5 flushes; Gallons per flush (label or measured): 1.6 gal; Laundry loads per week: 5 loads; Gallons per laundry load (label or example): 20 gal; Dishwasher loads per week: 4 loads; Gallons per dishwasher load (label or example): 4 gal; Faucet running minutes per day (whole household): 15 min; Faucet flow rate (label or measured): 1.5 gal/min; Outdoor use per week (irrigation, washing, pool top-up): 100 gal; Water price per 1,000 gallons (example): 6 $ per 1,000 gal.
Example result: Daily household use: 125.36 gal/day; Monthly use: 3,816 gal; Annual use: 45,787 gal; Per person per day: 41.79 gal; Monthly water cost: $22.89; Annual water cost: $274.72.

Two people, efficient fixtures, no outdoor use: People in the household: 2 people; Showers per person per day: 1 showers; Minutes per shower: 10 min; Shower flow rate (label or measured): 1.8 gal/min; Toilet flushes per person per day: 5 flushes; Gallons per flush (label or measured): 1.28 gal; Laundry loads per week: 3 loads; Gallons per laundry load (label or example): 15 gal; Dishwasher loads per week: 3 loads; Gallons per dishwasher load (label or example): 3.5 gal; Faucet running minutes per day (whole household): 10 min; Faucet flow rate (label or measured): 1.2 gal/min; Outdoor use per week (irrigation, washing, pool top-up): 0 gal; Water price per 1,000 gallons (example): 8 $ per 1,000 gal.
Example result: Daily household use: 68.73 gal/day; Monthly use: 2,092 gal; Annual use: 25,103 gal; Per person per day: 34.36 gal; Monthly water cost: $16.74; Annual water cost: $200.82.

Limitations and common mistakes

An estimate from the habits and flow rates you enter; use fixture labels or a bucket-and-timer measurement rather than guesses. Leaks, tiered or seasonal tariffs, fixed service charges, sewer charges and taxes are not included unless you fold them into the single price per 1,000 gallons. Compare with your meter reading or bill for the real figure.

Using a showerhead’s maximum rated flow when the real flow is lower, or the reverse with an old fixture. Time how long it takes to fill a bucket to get the actual gallons per minute.

Sources and assumptions

Method WATER-USAGE-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.