How is energy calculated?

Thermal energy = volume × specific heat × (mix temperature − cold inlet). We assume 1 kg/L and 4.186 kJ/kg·°C. Input (meter) energy divides by your water heater efficiency (or COP for heat pumps).

Do I need the hot water outlet temperature?

We use it to estimate the hot-water fraction used for mixing. The thermal energy to reach your chosen mix temperature is the same either way, but this fraction is informative and helps the model stay transparent.

No. Everything runs locally in your browser.

Shower Water & Energy Calculator — Litres, kWh, Cost & CO₂

Friendly, awareness-level estimates for planning and comparison. Private by design — runs locally in your browser.

Inputs

Units Temperature units Currency

🚿 Shower details

Shower flow Duration (minutes) Showers / person / day

Cold inlet temp Desired mix temp Hot outlet temp

Tip: A comfortable shower often uses ~38–41°C. Inlet varies by season.

🔥 Heater & energy

Heater preset Efficiency / COP Energy price (per kWh) CO₂ intensity (kg/kWh)

Efficiency is how much input energy reaches the water (COP>1 for heat pumps). Price and CO₂ are editable placeholders.

Advanced & presets (optional)

L per US gallon Low-flow example (L/min) Standard example (L/min) Power shower example (L/min)

Examples are references only; change your own numbers to match reality.

Awareness-level estimator. Real fixtures, pressures, seasons, and tariffs vary.

Results

What’s Being Calculated?

Water: flow × time = mixed water volume.
Thermal energy at the tap: volume × 1 kg/L × 4.186 kJ/kg·°C × (mix − cold).
Meter (input) energy: thermal ÷ efficiency (or ÷ COP for heat pumps).
Cost: meter kWh × price.
CO₂: meter kWh × kg/kWh.
Hot-water fraction (informational): (mix − cold)/(hot − cold), bounded 0–1.

Tips

Try a lower flow (e.g., 6–7 L/min) or shorter time. Small tweaks add up.
Colder inlet → more energy. Seasonal adjustments can be insightful.
Switch heater presets to compare electric, gas combi, or heat pump water heating.

Understanding Water, Energy, and Carbon in Showers

Showers are a daily habit for billions of people, but few realize how much water and energy go into every minute under the spray. The Shower Water & Energy Calculator helps you visualize these hidden flows by converting familiar inputs—flow rate, duration, and temperature—into measurable outcomes such as litres of water used, kilowatt-hours of energy to heat that water, and the resulting carbon footprint. It’s a practical way to connect comfort and convenience with sustainability awareness.

Heating water is often the most energy-intensive part of domestic water use. A typical eight-minute shower at 9 L/min can consume around 70 litres of water and 3 kWh of heat energy. That might not sound like much, but repeated daily, it adds up to more than 1,000 kWh per person each year—comparable to running a small electric heater for months. The calculator estimates this thermal energy using the physical relationship between water volume, specific heat, and temperature rise, while accounting for your chosen heater efficiency or heat-pump coefficient of performance (COP).

Small changes make a big difference. Reducing flow from 9 L/min to 6 L/min can save roughly one-third of the energy and water without noticeably reducing comfort, especially with modern efficient showerheads. Likewise, shortening a shower by two minutes or lowering the mix temperature slightly can yield meaningful savings in both cost and carbon emissions. The calculator’s live feedback encourages experimentation—helping you find a balance between wellbeing and efficiency.

Because all calculations run locally in your browser, no personal data or usage information is transmitted. The tool is designed for privacy, education, and transparency, giving you a clear picture of your household’s environmental impact without judgment or tracking. Whether you’re teaching students about energy flows, estimating your home’s footprint, or simply curious about everyday sustainability, this free web app provides a straightforward, science-based starting point.