Size a generator from measured or estimated running kilowatts, add motor starting current, apply power factor (typically 0.8) to convert to kVA, then add 15–25% headroom for growth and altitude. Never size only on nameplate kVA of a failed set. Use a load list, not a guess — then confirm with a site assessment before you buy.
Why this decision matters
Size a generator from measured or estimated running kilowatts, add motor starting current, apply power factor (typically 0.8) to convert to kVA, then add 15–25% headroom for growth and altitude. Never size only on nameplate kVA of a failed set. Use a load list, not a guess — then confirm with a site assessment before you buy. Buyers who skip structured sizing or compliance checks pay twice: once for the wrong unit, and again for downtime, fuel waste or a failed insurance claim.
AGP Generators engineers treat every enquiry as a load and site problem first, a product second. The notes below are the same framework we use on commercial RFQs across South Africa and SADC.
Practical method
Step-by-step
Start with a written load list: running watts, starting watts, duty cycle and which loads are truly critical. Convert watts to kVA using power factor (0.8 is the commercial default unless you know otherwise).
Apply site factors next — altitude derate, ambient temperature, fuel quality and whether the set will see prime hours or true standby. Only then shortlist engine brands and canopy types.
Validate with our Generator sizing calculator and a specialist review before you issue a purchase order. Catalogue pages for the 100 kVA Perkins silent and 30 kVA three-phase silent show real price bands excl. VAT to sanity-check budgets.
- Record running and starting loads separately for motors and compressors.
- Separate essential vs shedable circuits so you do not oversize the set.
- Confirm phase (single vs three) against the DB and utility supply.
- Document who owns installation, CoC and first service.
Reference data
Use the table as an indicative planning aid, not a substitute for a site assessment. Prices and fuel figures move with diesel wholesale rates and exchange rates — we re-verify commercial quotes at order stage. Last updated 2026-08-15.
Common mistakes
Copying the kVA of a failed set without measuring today’s load. Ignoring motor starting. Buying open-frame units for estate boundaries. Skipping changeover and earthing design. Assuming “silent” means inaudible indoors.
How AGP helps
We size, supply, install and maintain diesel and petrol generators from 2.2 kVA to 1000+ kVA. Request a quote with your load list, or call +27 41 007 0618. For hybrid and long-hour sites, ask about diesel-solar controllers that keep engines in an efficient band.
Data table
Indicative running load vs recommended kVA band
| Facility type | Typical running kW | Start-heavy? | Planning kVA |
|---|---|---|---|
| Home / small office | 4–8 | Low | 10–15 |
| Retail / clinic | 20–40 | Medium | 40–60 |
| Hotel 80 rooms | 55–75 | Medium | 100 |
| Light factory | 70–110 | High | 150–200 |
| Process / mine support | 180–350 | High | 250–500 |
Figures are indicative. Last updated 15 August 2026.
Frequently asked questions
Do I size in kW or kVA?
Generators are sold in kVA. Convert running kW ÷ power factor (often 0.8) then add starting and headroom.
How much headroom should I add?
Typically 15–25% after starting diversity, more at altitude or for near-term expansion.
Can I use the old generator’s kVA?
Only as a clue. Measure today’s load — equipment usually grows over a decade.
What about three-phase imbalance?
Large single-phase loads on one leg force upsizing or load redistribution.
Will the sizing calculator replace an engineer?
It speeds a first estimate. Critical sites still need a reviewed load assessment.
Related tools: Generator sizing calculator · All insights
Related sizes, categories and services: 100 kVA generators, 30 kVA generators and petrol generators.
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