Hot Water Usage Calculator
Estimate how much hot water a household uses in a day — showers, baths, basin use and appliances — in litres and US gallons.
How much hot water does a household actually use? It is showers, baths, basin use and appliances — added up, with the assumptions written down so you can see what they are.
Enter the day's usage; the total follows in litres and gallons.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Enter the number of showers, baths and basin uses per day.
- Enter the shower length and flow.
- Enter the appliance cycles and the household size.
- Read the daily total, the breakdown and the per-person figure.
Worked example
| Showers | 2 × 8 min × 9 L/min = 144 L |
|---|---|
| Baths | 1 × 80 L = 80 L |
| Basin | 3 × 5 L = 15 L |
| Appliances | 1 × 15 L + 1 × 50 L = 65 L |
| Total | 144 + 80 + 15 + 65 = 304 L (80.31 US gal) |
| Per person (4 people) | 304 ÷ 4 = 76 L |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How much hot water does a shower use?
Minutes × flow: an 8-minute shower at 9 L/min uses 72 litres. A power shower at 15 L/min uses 120 litres for the same 8 minutes. Enter your own flow if you know it.
How much water does a bath use?
About 80 litres for a typical bath (a full bath is 150+ litres; most people fill it about half). This calculator uses 80 L per bath.
How do I size a water heater from this?
Size the heater or tank for the daily total — plus a margin for guests and cold days. A household using 304 L/day needs at least that in storage or heating capacity. Use the water tank calculator for the tank size.
Are these figures exact?
No — they are estimates from documented assumptions. Real usage depends on the fittings installed: measure your shower flow and bath volume if you need precision.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.