Stop Guessing. Size Your Diesel Generator Right β in Seconds.
Power failures don’t wait. And neither should your backup plan.
But buying the wrong generator size costs you twice:
β Undersized? It trips under load.
β 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.
β‘ 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.
β οΈ 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: 0.6β0.8. Commercial: 0.7β0.9. Industrial: 0.8β1.0.
- 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 β”]
Understanding Your Results
After clicking “Calculate”, you’ll see three key outputs:
πΉ Running kVA Required: Continuous load your DG must handle.
πΉ Starting kVA Required: Peak demand when largest motor kicks in.
πΉ 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
β Altitude & Temperature: Generators lose ~3% capacity per 5Β°C above 25Β°C. High altitude? Add 1% derating per 100m above 1000m.
β Harmonic Loads: VFDs, UPS systems, and LED drivers create “dirty power”. May require 10β20% larger DG.
β Load Sequencing: Starting motors one-by-one reduces peak surge. Manual sequencing can save you a size tier.
β Fuel Type & Runtime: Diesel vs. gas vs. propane affects availability and runtime. Plan for 24β72 hour fuel storage.
Ready to Buy? Top Diesel Generators by Size Tier
| Recommended kVA | Best For | Top-Rated Models to Research |
|---|---|---|
| 20β50 kVA | Small workshops, clinics, homes | [Honda EU7000is], [DuroMax XP13000EH] |
| 62β150 kVA | Retail stores, offices, farms | [Cummins RS130], [Generac SD150] |
| 200β500 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 15β25% 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?”
