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Load Calculation For Building Calculator

Work out load calculation for building instantly with clear inputs, formula shown and shareable results.

About Load Calculation For Building Calculator

Building load starts from connected load — lighting and small power by area density plus HVAC and fixed equipment — then applies a demand factor to each category, because not everything runs simultaneously at full output. The resulting maximum demand is what sizes the supply and transformer.

Formula

Building load

connected = area x W/m2 + HVAC + equipment; maximum demand applies a factor per category

Worked example

With the default values below, Load Calculation For Building Calculator returns Total connected load of 71.25. Change any input above and every figure here is recalculated in your browser.

Inputs used

Floor area
450 m²
Lighting and small power density
25 W/m²
HVAC load
38 kW
Fixed equipment load
22 kW

Results

Total connected load
71.25 kW
Estimated maximum demand
55.93 kW
Supply current at 400 V
89.69 A
Overall load density
158.33 W/m²

Step by step

  1. 1Values used
  2. 2Building load
  3. 3Total connected load= 71.25 kW
  4. 4Estimated maximum demand= 55.93 kW
  5. 5Supply current at 400 V= 89.69 A
  6. 6Overall load density= 158.33 W/m²

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

What load density is typical?

Roughly 15-25 W/m2 for offices including small power, 40-80 W/m2 for retail with display lighting, and far more for data or catering areas.

Why not just size for connected load?

It would be grossly oversized and expensive. Diversity between categories and within them is real and is recognised by every wiring code.

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