Generator Sizing Calculator
Find the right generator KVA for your load and estimate running costs at current Nigerian fuel prices.
Your Power Load
Current Lagos diesel avg: ₦1,340/L · Petrol: ₦1,050/L
Recommended Generator Size
Running Costs
How to Choose the Right Generator Size in Nigeria
Choosing the wrong generator size is one of the most expensive mistakes Nigerian homeowners and business owners make. Buy too small and you'll overload it — damaging the machine and leaving appliances underpowered. Buy too large and you'll waste significant fuel running a generator at 30–40% capacity, which also causes wet stacking and accelerates engine wear. Getting the sizing right protects your investment and keeps running costs manageable.
The fundamental calculation starts with your total connected load in watts. Add up the wattage of every appliance you intend to run simultaneously — not just what's in the house, but what will actually be on at the same time. A well-equipped Nigerian home might run ceiling fans, a fridge, a TV, a water pump, phone chargers, and a few LED bulbs concurrently, totalling around 1,000–1,500 watts for a typical 3-bedroom flat without air conditioning.
Understanding KVA vs Kilowatts
Generators are rated in KVA (kilovolt-amperes), not kilowatts. The relationship between the two depends on your power factor — typically 0.8 for most household loads. This means a 5 KVA generator delivers around 4,000 watts (4 kW) of usable power. Always convert your watt total to KVA by dividing by 1,000 and then by 0.8 before sizing your generator. The calculator above handles this automatically.
Common Generator Sizes and Their Uses
- 1–1.5 KVA (I-Pass My Neighbour): Lights, fans, phone charging, small TV. Not suitable for fridges or pumps.
- 2.5–3.5 KVA: Standard home backup — lights, fans, fridge, TV, one window AC or a water pump (not simultaneously).
- 5 KVA: Comfortable home with one 1.5HP AC unit, fridge, and all lighting. The most popular choice for Lagos middle-class homes.
- 7.5–10 KVA: Heavy home loads (multiple AC units) or small offices with computers and printers.
- 15–25 KVA+: Commercial premises, petrol stations, larger offices, and industrial applications.
The 25% Buffer Rule
Industry best practice is to size your generator 20–25% above your calculated peak load. If your calculator result shows you need 3.5 KVA, buy a 5 KVA unit. This buffer has three benefits: it handles the surge current drawn by motors (fridges and pumps draw 3–6x their running wattage at startup), it accommodates future load additions, and it keeps the generator running at 70–80% capacity — the optimal efficiency range for most petrol and diesel generators.
Important: Running a generator consistently above 80% load shortens engine life, increases fuel consumption disproportionately, and risks tripping the circuit breaker during motor starts. Always leave headroom.
Fuel Costs: The Hidden Long-Term Expense
The purchase price of a generator is often dwarfed by its lifetime fuel cost. A 3.5 KVA generator running 10 hours daily at ₦1,050/L petrol costs roughly ₦500,000–₦600,000 per year in fuel alone — before oil changes, spark plugs, servicing, and eventual engine overhaul. Over five years, that's ₦2.5–₦3 million on a generator you may have bought for ₦150,000. This is why solar is increasingly compelling for households and businesses with high generator dependency. Use the Solar ROI Calculator to compare the true lifetime costs side by side.
Tip: Diesel generators are generally more fuel-efficient than petrol equivalents and better suited for heavy daily use (8+ hours). For occasional backup (2–4 hours), a petrol generator is cheaper to purchase and maintain.