Stop Guessing. Size Your Diesel Generator Right — in Seconds.
Power failures don’t wait. And neither should your backup plan.
But buying the wrong generator size costs you twice:
→ Undersized? It trips under load.
→ Oversized? You waste fuel, money, and maintenance.
That’s why we built this free DG Load Calculator. No signup. No spam. Just accurate, transparent sizing.
⚡ DG Load Calculator
Size your diesel generator with motor surge, demand factor & expansion margin
How This Generator Sizing Tool Works
Most online calculators oversimplify. Ours doesn’t.
We factor in what actually matters:
- Demand factor: Not all loads run at once. Smart.
- Power factor: Converts kW to real-world kVA.
- Motor starting surge: The #1 reason generators fail on startup.
- Expansion margin: Future-proof your investment.
- Standard sizing: Outputs match real-world DG models you can actually buy.
The result? A recommended kVA rating you can trust as a starting point.
⚠️ Important: This is a preliminary estimate. Always consult a licensed electrical engineer before final purchase. Site conditions, harmonics, and local codes affect final specs.
What You’ll Need Before Calculating
Gather these numbers first. It takes 5 minutes:
- Total connected load (kW): Sum of all equipment nameplate ratings.
Tip: Don’t add amps or HP directly. Convert first. - Demand factor: Residential: 0.6–0.8. Commercial: 0.7–0.9. Industrial: 0.8–1.0.
- Power factor: 0.8 is standard. Check motor nameplates if unsure.
- Largest motor: Identify the single biggest motor (pump, compressor, HVAC).
- Starting method: DOL? Star-delta? VFD? This changes surge dramatically.
[“Not sure about your load values? Try this clamp meter to measure actual current draw →”]
Understanding Your Results
After clicking “Calculate”, you’ll see three key outputs:
🔹 Running kVA Required: Continuous load your DG must handle.
🔹 Starting kVA Required: Peak demand when largest motor kicks in.
🔹 Recommended Standard Size: Next available commercial DG rating.
The breakdown section shows every step. No black box. No guesswork.
Example:
Input: 150 kW total load, 0.8 demand factor, 0.8 PF, 30 kW largest motor (DOL start)
Output: 200 kVA recommended
Why? Motor surge adds ~45 kVA temporarily. Expansion buffer adds 10%. Rounded to nearest standard size.
Critical Factors This Calculator Can’t See
❗ Altitude & Temperature: Generators lose ~3% capacity per 5°C above 25°C. High altitude? Add 1% derating per 100m above 1000m.
❗ Harmonic Loads: VFDs, UPS systems, and LED drivers create “dirty power”. May require 10–20% larger DG.
❗ Load Sequencing: Starting motors one-by-one reduces peak surge. Manual sequencing can save you a size tier.
❗ Fuel Type & Runtime: Diesel vs. gas vs. propane affects availability and runtime. Plan for 24–72 hour fuel storage.
Ready to Buy? Top Diesel Generators by Size Tier
| Recommended kVA | Best For | Top-Rated Models to Research |
|---|---|---|
| 20–50 kVA | Small workshops, clinics, homes | [Honda EU7000is], [DuroMax XP13000EH] |
| 62–150 kVA | Retail stores, offices, farms | [Cummins RS130], [Generac SD150] |
| 200–500 kVA | Factories, hospitals, data centers | [Caterpillar C18], [Kohler 500REZJB] |
Always verify specs with the manufacturer. Prices and availability change.
FAQs
Q: Is kVA the same as kW?
A: No. kW = real power. kVA = apparent power. Divide kW by power factor (usually 0.8) to get kVA. This calculator does it automatically.
Q: What if I have multiple large motors?
A: This tool accounts for the largest motor surge. If you have 2+ large motors starting simultaneously, add 15–25% buffer or consult an engineer.
Q: Can I use this for solar + generator hybrid systems?
A: Partially. This calculates generator-only capacity. For hybrids, factor in solar contribution and battery buffer.
Q: How often should I service a diesel generator?
A: Every 250 hours or 6 months (whichever comes first).
Related diesel generator sizing resources:
- Use the DG load calculator to estimate your baseline kW and kVA
- Read the full diesel generator sizing guide
- Learn the difference between ratings in the kW to kVA converter guide
- Fix startup overload issues in Motor Starting Surge: Why Your Generator Trips on Startup
- Compare products in the best diesel generators by kVA tier guide
- See how site conditions reduce output in generator derating explained
- Understand electronic load impact in generator sizing for non-linear loads
- See a real example in this hospital generator sizing case study
Final Thought: Don’t Let Power Uncertainty Hold You Back
The right generator isn’t about max specs. It’s about reliable specs.
Use this calculator to narrow your options. Then talk to a dealer. Test under load. Verify warranty terms.
Because when the grid fails, you won’t have time to Google “why is my generator smoking?”
