Shower Water, Energy and Cost Calculator

Calculate litres or gallons, heating kWh, water and sewer charges, total cost, and CO₂ for one shower, one person, or your whole household over time.

Your shower

Quick presets

Current assumptions: 8 minutes, 9 L/min, electrically heated stored water.

Basic shower use

Volume units Duration (minutes) Flow rate (L/min) Shower type / estimate Household size (people) Showers per person per day

I don’t know my flow rate

Look for a rated flow on the showerhead, its underside, packaging, manual, or product page. Actual flow varies with pressure, so a bucket test is better.

Container volume (L) Seconds to fill

Heater

Heater type Energy price (per kWh)

Stored electric water is heated before the shower and mixed at the outlet; it is not a direct electric shower.

Water and wastewater rates

Currency Water billing Water rate (per cubic metre) Water pricing basis Wastewater / sewer rate (per cubic metre) Sewer pricing basis

The default prices are illustrative examples, not current or universal tariffs. Enter the volumetric rates from your bills. Set sewer rate to 0 if it does not apply.

Advanced assumptions

Temperature units Cold inlet (°C) Shower mix / target (°C) Stored hot-water outlet (°C) Efficiency / COP Carbon intensity (kg CO₂e/kWh) Water specific heat (kJ/kg·°C) Water density (kg/L) Litres per US gallon

Example carbon intensity: 0.20 kg CO₂e/kWh. Replace it with the dated factor for your energy source and region; the 2025 UK government factors are linked in the methodology below.

Results

Compare a target shower

Target duration (minutes) Target flow (L/min) Target heater Target energy price (per kWh) Target carbon intensity (kg CO₂e/kWh)

Worked example using the live calculation

Calculation methodology and formulas

The calculator distinguishes heat delivered to the water from energy bought at the meter. Symbols: V = water volume (L), f = flow (L/min), t = duration (min), ρ = density (kg/L), c = specific heat (kJ/kg·°C), ΔT = temperature rise (°C), η = efficiency, and P = direct-electric power (kW).

Water volume
V = f × t

Thermal energy delivered to mixed water
Q_water = V × ρ × c × (T_mix − T_cold) ÷ 3,600 kWh

Boiler, cylinder or heat-pump input
Q_input = Q_water ÷ η. For a heat pump, η is its coefficient of performance (COP) and may exceed 1.

Direct electric shower
Q_input = P × t ÷ 60; f_achievable = P × η × 60 ÷ (ρ × c × ΔT). The tool flags a requested warm flow above this physical estimate.

Usage charges
water cost = V × water rate per litre
sewer cost = V × sewer rate per litre

Heating and total cost
heating cost = Q_input × energy price
total = water + sewer + heating

Carbon
CO₂e = Q_input × kg CO₂e per kWh

Annualisation
year = per shower × showers/person/day × people × 365; month uses 365 ÷ 12 days.

What is not included

This is a usage estimate. It does not add cylinder standing losses, distribution-pipe losses, water run while warming up, recirculation-pump energy, drain-heat recovery, tariff standing charges, taxes, tiered prices, fixed sewer charges, or non-shower household use. A direct shower may modulate power; the rated-power model assumes the entered power is used for the full shower.

Shower water and cost answers

How much water does a shower use?

Multiply flow by time. The table shows litres for common durations; actual flow depends on the fixture and water pressure.

Duration	Low 6 L/min	Standard 9 L/min	High 14 L/min
5 minutes	30 L	45 L	70 L
8 minutes	48 L	72 L	112 L
10 minutes	60 L	90 L	140 L
15 minutes	90 L	135 L	210 L

How much does a shower cost?

The complete usage cost is heating plus metered water and wastewater. Energy often depends strongly on the temperature rise; water and sewer charges depend on volume. Use bill rates rather than the illustrative defaults.

Typical shower flow rates

Use 6 L/min as a low-flow scenario, 9 L/min as a general mixer scenario, and 14 L/min as a high-flow or power-shower scenario—not as universal fixture ratings. US EPA WaterSense-labelled heads are limited to 2.0 US gpm (about 7.6 L/min), while the US standard-showerhead reference is 2.5 gpm.

Electric vs mixer showers

A direct electric shower heats the cold mains supply as water passes through it. Its kW rating limits how much flow can reach the target temperature, especially with colder winter inlet water. A mixer uses stored or boiler-heated hot water plus cold water; its purchased energy is estimated from delivered heat divided by heater efficiency or COP.

How to reduce shower costs

Compare a shorter duration, a measured lower-flow head, or a different water heater above. Check that comfort and safe temperature control remain suitable. Flow and duration reduce both water and heating use; heater changes affect heating cost and emissions but not shower volume.

Sources, assumptions and review

Methodology: transparent engineering estimate implemented and reviewed by the Starlight Robotics editorial team. Last reviewed: 16 July 2026. Default prices and carbon intensity are editable examples, not claims about current local tariffs.

US EPA WaterSense: showerhead flow — 2.0 US gpm WaterSense maximum and 2.5 US gpm standard reference.
USGS: specific heat capacity of water — about 4,184 J/kg·°C; the calculator uses editable 4.186 kJ/kg·°C.
USGS: water density and US gallon conversion — approximately 1 kg/L and 3.7854 L/US gal.
US Department of Energy: water-heater modes and efficiency context — source for resistance and heat-pump example ranges. Actual product performance varies.
UK Health and Safety Executive: shower temperature risk — temperatures above 44°C can create scalding risk for vulnerable people; temperature is an estimate, not safety control.
Triton: common 8.5, 9.5 and 10.5 kW direct-electric ratings — manufacturer examples and seasonal flow context.
UK government 2025 greenhouse-gas conversion factors — use the appropriate dated electricity or fuel factor instead of assuming the example applies universally.

Frequently asked questions

How many litres does an 8-minute shower use?

At 9 litres per minute, an 8-minute shower uses 72 litres. Multiply your measured flow rate by 8 for a more personal estimate.

How many litres does a 10-minute shower use?

At 9 litres per minute, a 10-minute shower uses 90 litres. A 6 L/min low-flow head would use 60 litres in the same time.

How much does one shower cost?

One shower costs the heating charge plus any metered water and wastewater charges. Enter your bill rates because the answer varies by heater, tariff, flow, duration and location.

How do I measure shower flow rate?

Catch the shower water in a container for a measured number of seconds. Flow per minute equals container volume multiplied by 60 and divided by the fill time.

What is a typical low-flow shower rate?

This calculator uses 6 L/min as a low-flow scenario. For context, US EPA WaterSense-labelled showerheads must use no more than 2.0 US gallons per minute, or about 7.6 L/min.

Is an electric shower the same as electrically heated stored water?

No. A direct electric shower heats incoming cold water while it flows, so its energy is power multiplied by time and its warm flow is power-limited. An electric cylinder heats stored water that is later mixed at the shower.

Does a shower use less water than a bath?

It depends on shower flow and duration and on the bath fill volume. Compare flow multiplied by minutes with the actual litres or gallons used to fill your bath.

Why may my actual bill differ?

Bills can include standing charges, tiered rates, taxes, pipe and cylinder losses, warm-up water and other household use that this usage estimate does not include.

Is my data uploaded?

No. The calculator runs locally in your browser. A share link contains only the input values placed in its URL.