Generator Sizing Guide

Size your generator correctly for reliable starts, stable voltage and efficient running. Use our load calculator to total your running kW, estimate starting demand (inrush), and get a suggested generator size in kVA.

Running load (kW) total Start demand estimate PF & headroom controls Copyable summary

Request a Quote Equipment Power Ratings Single Phase vs Three Phase

Sizing Quick Tips

If you’re unsure about a value, use conservative assumptions and we’ll verify for you:

PF: default 0.8 unless your equipment specifies otherwise.
Headroom: 10–20% is usually sensible for stability and growth.
Motors: use 2.0–3.0x start multiplier for pumps/compressors.
Three-phase: balance loads across phases where possible.

Note: The starting demand here is a guide. Sites with multiple large motors may need a deeper check (simultaneous starts, VFDs, soft starters, load steps).

Generator Load Calculator

Enter the equipment you need to run. The calculator totals your running load (kW), estimates a conservative starting demand, and suggests a generator size in kVA using your selected power factor and spare capacity.

Tip: Motors, pumps, compressors and refrigeration often need a higher start multiplier (e.g. 2.0–3.0). If you’re unsure, pick a higher value and we’ll help validate it.

Your Loads

Item

Qty

Running (kW)

Start Multiplier

Remove

Settings

Power Factor (PF)

0.80

Most generator sizing uses PF 0.8 unless specified. Spare Capacity

15%

Recommended: 10–20% headroom for growth and stability. Supply Type Three-phase loads should be balanced across phases for best performance.

Results

Total Running Load 0.0 kW

Estimated Starting Demand 0.0 kW

kVA Required (Running) 0.0 kVA

Recommended Generator Size 0 kVA

Why Generator Sizing Matters

Reliable motor starting: avoids nuisance trips and voltage dips on start-up.
Stable output: maintains voltage and frequency for sensitive electronics.
Better efficiency: reduces fuel waste from oversized sets.
Lower wear: prevents overload and excessive engine stress.
Future-ready: headroom for growth and changing site needs.

Understanding kVA vs kW

Generators are typically rated in kVA (apparent power) rather than kW (real power). A common sizing assumption is a power factor (PF) of 0.8.

Rule of thumb: kVA ≈ kW ÷ PF (e.g. 80 kW ÷ 0.8 = 100 kVA).

Typical Generator Size Guide

Typical Size Range
20–60 kVA (small sites, welfare, lighting, small plant)
60–150 kVA (farms, workshops, medium commercial loads)
150–500 kVA (industrial units, larger plant, multiple motors)
500 kVA+ (large sites, critical systems, heavy industry)