Maximum Demand & Diversity Calculator
Add the loads on a board, apply diversity, and get the maximum demand in amps and kVA, the balance across the three phases, and a suggested incomer rating. A first-pass estimate to BS 7671 and the IET On-Site Guide.
Diversity category factors are an indicative simplification — set the factor per load to match your design.
Diversity category factors here are a simplification of the full IET On-Site Guide / Guidance Note 1 method (which treats, for example, "the largest load plus a percentage of the remainder"). Use it for a quick estimate, then confirm the diversity applied for the actual installation before issue.
Why Maximum Demand Matters
Maximum demand sets the size of the incoming supply, the main switch and the submain cables — over-estimate and you pay for copper and supply capacity you never use; under-estimate and you trip the incomer. Diversity is the allowance that not every load runs at full power at once. This tool rolls the loads up per phase and flags an unbalanced board. For a full demand assessment across a distribution network, see our ProDesign cable calculation service, or read maximum demand & diversity to BS 7671.