Calculate your running cost
Change the example values to match your appliance, usage and electricity tariff. Results update instantly.
Estimated electricity costs
Important: Results depend on your entered assumptions. Actual power draw, energy consumption, tariffs and usage vary. Standing charges are excluded; these are estimates, not measured bills.
How it works
Ideal heat energy (kWh) ≈ litres × temperature rise in °C × 0.001163 (using water near 1 kg/L). Divide by the assumed overall heat-transfer efficiency to estimate electricity needed. Heating time ≈ electricity needed ÷ heater power in kW. Cost = kWh × your unit rate.
Worked UK example
Example: raising 150 litres from 15°C to 60°C needs about 7.85 kWh of heat. At an illustrative 95% overall efficiency that is about 8.26 kWh of electricity, or £2.17 at 26.32p/kWh. A continuously powered 3 kW heater would take roughly 2.75 hours.
Before relying on your estimate
This estimates heating an entire specified water volume from the initial to target temperature. A real hot-water cylinder may heat only part of the tank, start with warmer water, stratify or lose heat while stored; a thermostat may stop the element early. This is not a forecast of your whole hot-water bill.
Common questions
Does a 3 kW heater use less electricity than a 6 kW heater?
For the same water temperature rise and similar losses, the required energy is broadly similar. Higher rated power mainly shortens heating time.
Does this estimate daily standing losses?
No. It estimates one specified warm-up. Extra cylinder heat loss, hot-water draws and thermostat cycling may increase real-world electricity use.
Which electricity price should I enter?
Your unit rate in pence per kWh appears on your energy bill or tariff information. The starting value is illustrative and should be replaced with your actual rate. Visit Ofgem for official energy price information.