What is the Shower Cost Calculator?
This calculator estimates how much one shower really costs by combining the price of the water you use with the energy needed to heat it. Enter your shower head flow rate, how long you shower, and your local water and energy prices, and it returns the cost per shower, per day and per year, plus the litres of water and kilowatt-hours of energy involved. The tool is currency-neutral — just enter prices in whatever currency you pay (per litre for water and per kWh for energy).
How to use it
Find your flow rate from the shower head label (typical mains showers are 8–12 L/min; eco heads can be 6 L/min or less). Enter your usual shower time, set your cold inlet temperature and the temperature you shower at, then add your water and electricity/gas unit prices. Adjust "showers per day" if more than one person showers. The results update for a single shower and scale up to daily and yearly totals.
The formula explained
Litres used = flow rate \(\times\) minutes. Heating water from a cold inlet temperature to your shower temperature requires energy according to the specific heat of water (about 4.186 kJ per kilogram per °C; 1 litre ≈ 1 kg). Dividing kilojoules by 3600 converts to kWh. The total cost is the water charge plus the energy charge: $$\text{Cost} = \text{litres} \times \text{water price} + \text{kWh} \times \text{energy price}$$ Real heaters are not 100% efficient, so actual gas/electric bills can be slightly higher.
Worked example
A 9 L/min head used for 8 minutes uses 72 litres. Heating from 15 °C to 40 °C is a 25 °C rise: energy $$= \frac{4.186 \times 72 \times 25}{3600} \approx 2.093 \text{ kWh}.$$ At 0.002 per litre, water costs 0.144; at 0.30 per kWh, heating costs about 0.628. Total ≈ 0.772 per shower, or about 282 per year for one shower a day.
FAQ
Does it account for heater efficiency? No — it assumes the energy reaches the water. Divide energy cost by your heater's efficiency (e.g. 0.9) for a more conservative estimate.
Why include cold water temperature? The colder the incoming water, the more energy is needed to reach shower temperature, which raises the cost.
What units should I use? Litres per minute for flow, and prices per litre and per kWh. The result is in the same currency as your prices.
