Shower Cost Calculator

What does this calculator do?

The Shower Cost Calculator turns a showerhead's flow rate, shower duration, and how much you heat the water into real numbers: liters of water used, kilowatt-hours of energy burned heating it, and what that costs — as a total and per shower. Run it for one shower or for a household's worth over a week to see where the hot-water bill actually comes from.

How the numbers are worked out:

1. Water used: waterLiters = flowRateLpm × durationMinutes × showers (1 liter of water weighs ≈ 1 kg).
2. Energy to heat it: energyKwh = waterLiters × 4.186 × temperatureRiseC ÷ 3600 — 4.186 kJ/kg°C is water's specific heat, and 3600 kJ makes 1 kWh.
3. Water cost: (waterLiters ÷ 1000) × waterCostPer1000L.
4. Energy cost: energyKwh × energyCostPerKwh.
5. Total cost is water cost plus energy cost; cost per shower divides that total by the shower count.

Worked example: a 9 L/min showerhead run for 8 minutes uses 9 × 8 × 1 = 72 L. Heating that 30°C takes 72 × 4.186 × 30 ÷ 3600 ≈ 2.51 kWh. At $2.50 per 1,000 L and $0.16/kWh, that's about $0.18 in water, $0.40 in energy, and $0.58 total for the one shower.

How to use it

1. Enter the showerhead's flow rate in liters per minute (a standard head runs 8–12 L/min; low-flow heads go under 8).
2. Enter the duration per shower in minutes.
3. Set the number of showers to total up — leave it at 1 for a single shower, or raise it to model a household's showers over a day or week.
4. Enter the water temperature rise — how many degrees the water is heated above the cold-water temperature coming into the tap.
5. Enter your water cost (per 1,000 L) and energy cost (per kWh) from your utility bills.

The table updates as you type, and you can copy or download it as CSV.

Where do I find these rates?

Water cost is on your water utility bill, usually as a price per 1,000 liters or per cubic meter (1 m³ = 1,000 L, so the same number works either way). Energy cost is on your electricity (or gas-equivalent) bill as a price per kWh. Both fields are currency-agnostic — enter your local price and the costs come out in that same currency; the "$" shown is just a label.

What temperature rise should I use?

It's the difference between your incoming cold-water temperature and your shower temperature, not the shower temperature itself. Cold tap water is commonly 10–20°C depending on climate and season, and a comfortable shower is around 38–42°C — so a rise of 25–30°C is a reasonable default for most homes. Colder climates or winter months push the rise higher.

Why doesn't this match my actual water heater's energy use?

This models the theoretical energy needed to raise the water's temperature, at 100% efficiency. Real water heaters lose some energy to standby heat loss, pipe heat loss, and heating-element/burner inefficiency, so actual energy use is usually somewhat higher than this estimate. Treat it as a solid lower bound, not a substitute for a metered reading.

Privacy

This calculator runs entirely in your browser. Your flow rate, duration, shower count, and rates are never sent to a server, logged, or stored — the math happens locally on your device.