Water Usage Calculator
Estimate your household water use from showers, toilets, laundry and outdoor watering.
Last updated · View algorithm, constants and default inputs (JSON)
Comparison
About this calculator
This estimate includes only the shower, toilet, laundry, and outdoor inputs shown. Laundry and outdoor use are household totals divided equally across the people entered for the per-person result. It excludes sinks, faucets, leaks, dishwashers, and other uses. The cost applies your USD rate per 1,000 US gallons and excludes sewer charges, fixed fees, and taxes.
Worked example
calculated with the default values below
People in the household 4 · Showers per person per week 7 · Minutes per shower 8 min · Showerhead flow rate 2 gpm · Toilet flushes per person per day 5 · Gallons per flush 1.28 gal · Laundry loads per week 5 · Outdoor water per week (US gal) 200 gal · Rate (USD per 1,000 US gal) 4.5 USD/1,000 gal Daily household use 128.9 gal · Monthly household use 3,923 gal · Monthly water cost 17.65 USD · Yearly water cost 211.86 USD · Gallons per person per day 32.2 gal
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
G = p × n_s ÷ 7 × m_s × q_s + p × n_f × g_t + n_l ÷ 7 × 15 + G_o ÷ 7
- p
- People in household
- n_s
- Showers per person/week
- m_s
- Shower length (min)
- q_s
- Shower flow (gal/min)
- n_f
- Flushes per person/day
- n_l
- Laundry loads/week
Also uses gallons per flush (g_t) and outdoor US gallons/week (G_o). The per-person daily figure divides all household use equally by p. Monthly = daily×30.44; cost = monthly US gal ÷1,000 × USD rate.
Frequently asked questions
How does the monthly water cost get worked out from my usage?
Daily gallons are summed from the shower, toilet, laundry, and outdoor inputs, then multiplied by 30.44 for a monthly estimate. At $4.50 per 1,000 US gallons, 70 gallons/day is about $9.59 per month. For the per-person figure, household laundry and outdoor use are divided equally among the entered number of people. Sinks, leaks, sewer charges, and other unmodeled use are excluded.