Power Consumption Calculator — kWh and Running Cost at UK Rates

Power consumption is the amount of electrical energy an appliance or device uses over a period of time. It is measured in kilowatt-hours (kWh), which is the standard unit used on electricity bills. One kWh is the energy consumed by a 1,000-watt appliance running for one hour — or equivalently, a 100-watt appliance running for 10 hours.

For electricians, understanding power consumption is essential for several reasons. When designing circuits, you need to know the load each appliance draws to calculate the maximum demand of an installation. When advising customers, you can explain the running cost of different appliance choices — for example, comparing the cost of an electric shower versus a combi boiler, or an old storage heater versus a modern heat pump.

The power consumption calculator converts between watts, kilowatts, amps, and kWh, and calculates running costs at the current UK electricity rate. It is a straightforward tool but one that electricians and customers use frequently — particularly when discussing EV charger costs, solar panel savings, or the economics of replacing old electrical equipment with more efficient alternatives.

The calculator links directly to the circuit breaker sizing calculator when you need to move from power consumption assessment to circuit design.

The conversion from wattage to kilowatt-hours is straightforward but is the most commonly requested calculation in energy assessment:

For example, an electric radiator rated at 2,000W (2kW) running for 8 hours per day:

This calculation assumes the appliance runs at full power for the stated duration. In reality, many appliances cycle on and off (such as a fridge or thermostatically controlled heater), so the actual consumption may be lower than the rated wattage would suggest. The power consumption calculator allows you to enter both the rated wattage and an estimated duty cycle to give a more accurate result.

Electricity prices in the UK are regulated by the Energy Price Guarantee, which sets a cap on the unit rate and standing charge that energy suppliers can charge domestic customers. As of early 2026, the typical UK electricity rate is approximately 24.5p per kWh, though this varies by supplier, tariff type, and payment method.

The standing charge (approximately 55-60p per day) is a fixed daily fee regardless of consumption. This means the effective cost per kWh is higher for low-consumption households. For electricians advising customers on solar panel installations or EV charger economics, understanding the tariff structure is essential for accurate cost-benefit calculations.

Understanding the power consumption of common household appliances helps electricians advise customers on energy efficiency, circuit loading, and the economics of equipment upgrades. Below are typical consumption figures for common UK household appliances:

These figures assume typical UK usage patterns. Actual consumption varies with individual usage habits. The Elec-Mate power consumption calculator includes a database of common UK appliances with preset wattages, so you can quickly estimate the total household consumption or compare alternatives for your customers.

As electricians, customers frequently ask for advice on reducing their electricity bills. The power consumption calculator helps you quantify the savings from different efficiency measures:

• LED lighting: Replacing 10 old 60W incandescent or halogen bulbs with 8W LEDs saves approximately 1,900kWh per year (assuming 5 hours daily use) — that is approximately £465 at current rates.
• Smart controls: Installing timers and smart switches on immersion heaters, storage heaters, and other high-consumption appliances can reduce unnecessary operation by 20-30%.
• EV smart charging: Charging an EV on an off-peak tariff (7-10p per kWh) instead of the standard rate (24.5p) can save over £600 per year for a typical 10,000-mile driver.
• Solar PV: A 4kWp solar panel system generating 3,600kWh per year with 40% self-consumption saves approximately £350 per year plus export income.
• Standby elimination: Using switched socket strips and turning off appliances at the wall can save 300-500kWh per year (£75-£125).

The electrical calculator suite in Elec-Mate includes energy efficiency calculations alongside the standard BS 7671 tools, giving you a comprehensive toolkit for both installation work and customer advisory.