Your result
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Enter your values, then click Calculate result.How this calculator helps
Estimate a starting generator rating by combining continuous running watts with the largest additional startup surge. A safety allowance is added before converting real power to approximate kVA at a typical 0.8 power factor.
How to use it
- 1
Add the running watts of equipment expected to operate together.
- 2
Identify the largest additional motor or compressor startup surge.
- 3
Apply safety headroom and confirm the result with generator and equipment suppliers.
Formula and methodology
Required watts = running load + largest additional startup surge. Recommended kVA = required watts × safety factor ÷ 1,000 ÷ power factor.
Uses the values you enter with transparent energy, power and efficiency relationships. Provider tariffs and equipment specifications should be replaced with current figures.
Worked calculation example
A 3,000 W running load with a 1,500 W additional motor surge and 25% headroom needs about 7.0 kVA at 0.8 power factor.
How to interpret your result
Estimate minimum generator kVA from running load, largest startup surge and safety headroom. Read the main result together with the supporting values rather than treating one number as a guarantee. The disclosed method is: Required watts = running load + largest additional startup surge. Recommended kVA = required watts × safety factor ÷ 1,000 ÷ power factor.
Input guide
Add the running watts of equipment expected to operate together.
Identify the largest additional motor or compressor startup surge.
Apply safety headroom and confirm the result with generator and equipment suppliers.
Scenario comparison
| Scenario | What it demonstrates |
|---|---|
| Worked baseline | A 3,000 W running load with a 1,500 W additional motor surge and 25% headroom needs about 7.0 kVA at 0.8 power factor. |
| Motor starting check | ACs, pumps and refrigerators can briefly demand several times running power. |
| Power quality stress test | Sensitive electronics and nonlinear loads may require more conservative sizing. |
Common mistakes to avoid
- Ignoring motor starting: ACs, pumps and refrigerators can briefly demand several times running power.
- Overlooking power quality: Sensitive electronics and nonlinear loads may require more conservative sizing.
- Failing to test site conditions: Altitude, heat, fuel quality and continuous-duty rating affect available output.
Compare the result with a recent provider bill, the equipment nameplate and current NEPRA or distribution-company information.
What can affect the result?
Motor starting
ACs, pumps and refrigerators can briefly demand several times running power.
Power quality
Sensitive electronics and nonlinear loads may require more conservative sizing.
Site conditions
Altitude, heat, fuel quality and continuous-duty rating affect available output.
Limits of this estimate
This simplified estimate assumes 0.8 power factor and cannot account for every surge sequence, phase balance, derating or manufacturer requirement.
Sources and review information
Frequently asked questions
Is the generator size calculator free?＋
Yes. SolvePilot tools are free, work in your browser, and require no account.
Does SolvePilot store my values?＋
No. Calculations run locally in your browser and the values you enter are not sent to a server.
Should I treat the result as an exact bill or quotation?＋
No. Results are informed estimates. Final charges can vary because of taxes, tariffs, lender terms, usage patterns, or provider rules.
How can I improve the accuracy?＋
Use recent values from your own bill, statement or institution, review every assumption, and confirm important results with the relevant official source.
Should every appliance surge be added together?＋
Usually the largest coincident startup event matters, but equipment sequencing and simultaneous starts require professional review.