Electrical Load Calculator — Domestic Property

Connected load is the total wattage of all appliances if they were all running at full power simultaneously. Maximum demand applies diversity factors — the realistic expectation of simultaneous usage. For example, you are unlikely to use the kettle, oven, shower, and EV charger all at the same time. As a rough rule of thumb, the diversified maximum demand of a typical domestic property often works out around 40-60% of its connected load, though the exact ratio depends entirely on which appliances you have.

As a rule of thumb, a typical 3-bed UK house without electric heating has a diversified maximum demand of roughly 15-20kW (around 65-87A) — though the actual figure depends on your appliances and should be calculated, not assumed. Add an electric shower (9.5kW) and EV charger (7kW) and demand can climb toward 30kW or more, which may exceed a standard 100A supply. Older properties with a 60A or 80A supply may need an upgrade. For a circuit-by-circuit assessment using the IET On-Site Guide Table A2 diversity allowances, use our Maximum Demand Calculator.

Average daily energy consumption is different from peak demand. A typical UK household uses roughly 7-10 kWh of electricity per day (Ofgem's typical domestic consumption value falls to 2,500 kWh per year — about 6.8 kWh per day — from July 2026), but peak instantaneous demand can be far higher. A kettle alone draws 3kW, an electric shower 8.5-10.5kW, and an EV charger 7kW. This calculator estimates peak simultaneous load for sizing the supply, not average consumption for billing.

It depends on your existing demand and supply. A 7kW EV charger adds 32A continuous load. If your existing maximum demand is 60A and your main fuse is 80A, you may be fine. If demand exceeds your main fuse, you need to contact your DNO for a supply upgrade. Load management devices can help by reducing the charger output when other loads are high. Use our EV Charger Cable Sizing Calculator for detailed cable and protection requirements, and our Consumer Unit Sizing Calculator to check your board has capacity.

Diversity factors are multipliers (0 to 1) that represent the probability of an appliance being in use at peak time. A fridge runs continuously (factor 1.0), but a kettle is only on for minutes at a time (so a low factor is used). These factors prevent oversizing the electrical supply. Note: the per-appliance factors in this calculator are simplified usage estimates, not standard values. BS 7671 does not itself list diversity figures — the IET On-Site Guide Table A2 gives diversity allowances by circuit type (lighting, cooking, socket circuits, showers, etc.), while Table A1 gives the assumed current demands. For a Table A2 circuit-by-circuit calculation, use our Maximum Demand Calculator.