Generator Size Calculator — South Africa
Calculate the minimum generator kVA for any SA application. Accounts for motor starting surges and recommends standard South African generator sizes.
Quick answer: This generator sizing calculator finds your kVA. Add up the wattage of every appliance you want to run simultaneously, divide by a power factor of 0.8 to get running kVA, then add a 25% safety margin. For motor loads — fridges, pumps, aircons — multiply running watts by 3 to account for the starting surge before sizing your generator.
| Appliance | Watts (W) | Qty | Load Type | Running (W) |
|---|
⚠️ For planning purposes only. Generator connections to fixed wiring in SA must be done by a registered electrician with a manual changeover switch. Never connect a generator directly to your DB board without proper isolation.
How to Use This Generator Sizing Calculator
Six common loads (lights, router, TV, laptops, fridge, microwave) are pre-filled to start. Use the quick-add buttons for other common SA appliances — geyser, stove, pool pump — to skip typing them in, or add a custom line for anything else with its running watts and quantity. Mark each as Resistive (lights, electronics, heating elements) or Motor (fridge, pumps, aircon, compressors) — motor loads get a starting-surge multiplier applied automatically.
Leave power factor at 0.8 for a typical mixed home, and safety margin at 25% (recommended). The calculator shows your running and peak starting kVA, then recommends the next standard SA generator size up.
Generator Sizing for South Africa — The Formula
Generator sizing for load shedding or standby power in South Africa involves three steps: calculating running load, accounting for motor starting surges and applying a safety margin. Undersizing a generator leads to overloading, voltage collapse and shortened engine life. Oversizing wastes fuel and capital — a generator running at less than 30% load for extended periods also "wet stacks" (carbon buildup in diesel engines). The same generator sizing method applies whether you're comparing standard generator sizes for occasional load shedding backup or specifying a permanent standby installation.
Running kVA = Total running watts ÷ (Power Factor × 1000)
Peak kVA = (Resistive watts + Motor watts × 3) ÷ (Power Factor × 1000)
Min required = max(Running kVA, Peak kVA)
With margin = Min required × Safety factor (1.25 standard)
Select = Next standard size above "With margin" kVA
Understanding the motor starting surge
Electric motors — fridges, pool pumps, borehole pumps, air conditioners, compressors — draw 5–8 times their running current during the first 1–3 seconds of startup. This is called the locked rotor current or starting surge. The generator must supply this peak without its voltage collapsing below approximately 80% of nominal — otherwise the motor won't start and may burn out trying.
This calculator uses a conservative ×3 multiplier for motor starting kVA, which is appropriate for single-phase motors without soft-starters. Three-phase motors with star-delta starters or VFDs have a much lower starting surge (1.5–2×) and may allow a smaller generator — consult the equipment manufacturer's data.
Standard Generator Sizes in South Africa (2026) — kVA Reference Table
| Size | Real Power (0.8 PF) | Typical Use | Fuel | Approx Price (2026) |
|---|---|---|---|---|
| 3.5 kVA | 2.8 kW | Lights, TV, laptop, router, kettle | Petrol | R3,500–R6,000 |
| 5 kVA | 4.0 kW | Above + small fridge, 1–2 rooms | Petrol/Diesel | R5,500–R12,000 |
| 6.5 kVA | 5.2 kW | Average home backup, small AC | Petrol/Diesel | R7,000–R18,000 |
| 8 kVA | 6.4 kW | Larger home, pool pump, AC | Diesel | R15,000–R28,000 |
| 10 kVA | 8.0 kW | Large home, borehole, multiple AC | Diesel | R22,000–R40,000 |
| 15 kVA | 12.0 kW | Small business, farm, full house | Diesel | R35,000–R60,000 |
| 20 kVA | 16.0 kW | Medium business, complex supply | Diesel | R55,000–R100,000 |
Prices are indicative retail ranges for 2026. Diesel units are rated for continuous duty; petrol units are standby-rated. Always verify with your supplier.
Load Shedding Generator Planning — South African Context
What loads matter most during load shedding?
For typical South African load shedding of 2–4 hours per slot, most households prioritise: lights, Wi-Fi router, TV/decoder, laptop chargers and keeping the fridge cold. A fridge cycling on during generator use is the most common cause of undersized generator problems — it has both a motor load and a compressor starting surge. Always include the fridge in your load list.
Automatic vs manual changeover
South African electrical regulations (SANS 10142) require a manual changeover switch (or automatic transfer switch with anti-paralleling interlock) between your generator and the grid. You cannot simply plug a generator into a wall socket or connect it directly to your DB board — this back-feeds the street transformer and creates a lethal hazard for Eskom technicians. A registered electrician must install the changeover, and a CoC is required.
Petrol vs diesel — which is right for South Africa?
For load shedding at Stage 2–4 (2–4 hours per day), a petrol generator is cheaper to buy, quieter and easier to maintain. The fuel cost is higher per kWh but acceptable for occasional use. For Stage 5–6 or full backup on a farm or business, a diesel generator delivers 30–40% better fuel efficiency, longer service intervals and is rated for continuous operation. Diesel also stores more safely and for longer periods than petrol. For South African load shedding sizing: Stage 2 means 2 slots of approximately 2.5 hours per 24-hour cycle; Stage 4 means 4 slots (approximately 10 hours without power per 24 hours); Stage 6 means up to 6 slots (approximately 14–16 hours without power daily). A generator sized for Stage 4 coverage must be capable of running continuously for 3–4 hours per session. At Stage 6 — the most severe schedule Eskom operates — commercial premises may require a generator sized for near-continuous operation during business hours, with an automatic transfer switch to manage the changeover safely.