Electrical Load Calculator — estimate electrical load for your project. Fast, accurate, free. No signup required.
An electrical load estimate starts with the connected demand of appliances, heating, lighting, and charging equipment, then applies a diversity factor to reflect that not every load operates at full power at the same moment. The Electrical Load calculator keeps the topic-specific quantities visible so you can audit the assumptions before using the result.
Construction estimates are highly sensitive to site conditions, product specifications, local policy, and the stage of design. A useful early estimate states its units, boundary, design allowance, and source of any reference value. It should help you ask a better question of a supplier, designer, building-control officer, planning authority, or installer—not pretend that a three-field calculation is a signed design.
Use the related construction calculator for an adjacent check and the companion standards calculator when the result crosses into quantities, structure, services, energy, water, or regulation. Keep the original dimensions and assumptions with the displayed output so a later revision can be compared on like-for-like terms.
Where the page gives a consent, fire, electrical, accessibility, heritage, or safety prompt instead of a single number, that is deliberate. Those topics depend on documents, inspections, local rules, tested products, and professional judgement. The calculator can organise the first pass, but it cannot issue an approval or replace a competent person's review.
Diversified demand (kW) = connected load (kW) × diversity factor (% ÷ 100); current (A) = demand (kW) × 1,000 ÷ supply voltage (V).
The formula is intentionally shown beside the inputs. Convert millimetres, metres, kilowatts, amps, percentages, and category scores consistently, and keep intermediate precision until the final display. A plausible-looking answer can still be unusable if a clear opening was confused with an outside frame, a nominal capacity with a tested rating, or a planning assumption with a statutory threshold.
For site work, the formula is the beginning of the check rather than the complete specification. Add the conditions that control the real decision: subgrade and drainage for roads, grouping and installation method for cables, weather and emitter temperature for heat pumps, significance for heritage, occupancy for escape, and local policy for planning matters.
Inputs used here: connected load, diversity factor, and supply voltage. Keep each input traceable to a drawing, survey, test result, product sheet, policy document, or clearly marked planning assumption.
The diversified demand is an early-stage maximum-demand estimate. It can help compare a proposed installation with a service capacity, but it does not replace a load schedule that identifies start-up currents, motor loads, harmonics, phases, and protective-device coordination.
Check direction and order of magnitude before relying on the result. A larger opening should increase area, a longer cable should increase voltage drop, a higher COP should reduce electrical input, a wider exit should increase the indicative capacity, and a higher traffic class should demand a stronger cover or pavement solution. If a change behaves the other way, recheck the units and the field mapping.
Do not report more precision than the survey or input supports. Round a procurement quantity up where the supplier sells discrete sizes, preserve the unrounded design calculation for review, and label any result based on a default rate or simplified weighting. If the number affects structural stability, fire safety, electric shock protection, accessibility, legal consent, or a regulated rating, stop at the estimate and obtain the appropriate review.
Electrical design, alterations, and certification must be completed by a competent electrician to BS 7671 and applicable Building Regulations requirements. This calculator provides preliminary educational guidance only and does not constitute a structural design, electrical certificate, fire strategy, planning decision, Building Regulations approval, heritage consent, accessibility audit, or certified sustainability assessment.