Daily Water Usage Calculator Formula

Understand the math behind the daily water usage calculator. Each variable explained with a worked example.

Use the Daily Water Usage Calculator

Formulas Used

Daily Water Usage

daily_total = shower_gal + toilet_gal + other_gal

Monthly Usage

monthly_total = (shower_gal + toilet_gal + other_gal) * 30

Annual Usage

annual_total = (shower_gal + toilet_gal + other_gal) * 365

Shower Share

shower_pct = shower_gal / (shower_gal + toilet_gal + other_gal) * 100

Variables

VariableDescriptionDefault
shower_minTotal Shower Minutes per Day(minutes)16
shower_gpmShowerhead Flow Rate(gal/min)2.5
toilet_flushesToilet Flushes per Day10
toilet_gpfGallons per Flush(gallons)1.6
other_galOther Daily Use (faucets, laundry, dishes)(gallons)40
shower_galDerived value= shower_min * shower_gpmcalculated
toilet_galDerived value= toilet_flushes * toilet_gpfcalculated

How It Works

How to Calculate Daily Water Usage

Household water use can be broken down by fixture and activity.

Average Usage

  • Showers: 2.0-2.5 gal/min (17% of indoor use)
  • Toilets: 1.6 gal/flush (24% of indoor use)
  • Faucets: 15-20 gal/day
  • Clothes washer: 15-30 gal/load
  • Dishwasher: 6-10 gal/load

    • Formula

    Daily Total = Shower + Toilet + Other

    The average American uses about 80-100 gallons per day indoors.

    Worked Example

    A household with 16 min of showers, 10 flushes, and 40 gal other daily use.

    shower_min = 16shower_gpm = 2.5toilet_flushes = 10toilet_gpf = 1.6other_gal = 40
    1. 01Shower: 16 * 2.5 = 40 gallons
    2. 02Toilet: 10 * 1.6 = 16 gallons
    3. 03Other: 40 gallons
    4. 04Daily total: 40 + 16 + 40 = 96 gallons
    5. 05Annual: 96 * 365 = 35,040 gallons

    Ready to run the numbers?

    Open Daily Water Usage Calculator