Calculate Generator kVA Rating, Fuel Consumption & Cable Size
💡 Formula: kVA = (Load × PF) / Efficiency | Recommended kVA = kVA × (100% + motor factor)
kVA = (W × PF) / Eff | Fuel = 0.2 × kVA × Hrs (Diesel)
📖 Generator Size Calculator
This tool helps you select the right generator for your application. It calculates the required kVA rating, fuel consumption, and cable size based on your load, power factor, motor starting requirements, and altitude. Essential for backup power planning and industrial generator selection.
📐 Generator Sizing Formulas
Generator kVA: kVA = (Load × PF) / Efficiency Motor Starting kVA: kVA_start = (Motor kW × PF × Start Factor) / Eff Fuel Consumption (L/hr): Fuel = 0.2 × kVA (diesel) Cable Size: Based on current and distance
Where: Load = Total Connected Load (Watts) PF = Power Factor Efficiency = Generator Efficiency (%) Start Factor = Motor Starting Multiplier
📊 Standard Generator Sizes
kVA
kW (PF=0.8)
Typical Application
Fuel (L/hr)
5
4
Small Home
1.0
10
8
Home + Small Office
2.0
20
16
Medium Home
4.0
30
24
Large Home / Shop
6.0
50
40
Small Industrial
10.0
75
60
Medium Industrial
15.0
100
80
Large Industrial
20.0
150
120
Commercial Building
30.0
200
160
Large Commercial
40.0
300
240
Industrial Plant
60.0
500
400
Heavy Industrial
100.0
📌 Generator Sizing Recommendations
Calculate running load: Sum of all continuous loads
Consider starting current: Motors require 3-7× running current
Add 25-30% margin: For future expansion and peak loads
Altitude derating: Generators lose capacity at high altitude
Automatic Transfer Switch (ATS): For automatic backup
💡 Fuel Consumption Guide
Load (%)
Fuel Consumption (% of full load)
100%
100%
75%
85%
50%
65%
25%
40%
🔧 How to Use This Calculator
Enter total load (watts) - sum of all connected devices
Enter power factor - typical 0.85 for mixed loads
Select generator efficiency - 80-95%
Select motor starting type - affects starting current
Enter largest motor (kW) - for starting current calculation
Select altitude - derating factor
Results include recommended kVA, fuel consumption, and cable size
❓ Frequently Asked Questions (FAQ)
❓ How to size a generator for home? ▼
Calculate total load in watts, add 25% margin, divide by PF to get kVA. For 5kW load, you need 5/0.85 = 5.9 kVA → choose 6.5-7.5 kVA generator.
❓ What size generator for 5000W load? ▼
For 5000W at 0.85 PF, you need 5000 × 0.85 / 0.85 = 5000 VA = 5 kVA. Choose 6-7 kVA generator for safety.
❓ How to calculate generator fuel consumption? ▼
Diesel generator fuel consumption ≈ 0.2 L per kVA per hour. A 10 kVA generator uses about 2 L/hour at full load.
❓ What is the difference between kVA and kW? ▼
kVA is apparent power, kW is real power. kW = kVA × PF. For PF 0.8, 10 kVA = 8 kW.
❓ Why is motor starting important for generator sizing? ▼
Motors draw 3-7× running current during startup. The generator must handle this peak current. This calculator accounts for motor starting requirements.
❓ How does altitude affect generator performance? ▼
At higher altitudes, air density decreases, reducing engine power output. Derate generator capacity by 3-4% per 300m above sea level.