Generator-Größenrechner
Nenn- und Anlaufleistung mit Planungsreserve an typische Stufen anpassen. Nur Schätzung.
Summe gleichzeitiger Lasten — Nennwerte.
Schlimmster gleichzeitiger Fall. Leer bei rein ohmsch.
Auf Dauer und Spitze. Häufig 10–25 %.
kVA-Hinweis aus Spitze.
Table of Contents
Nur Planung
Generators are sized for continuous (running) output and short-duration starting (surge) capability. Undersizing causes trips or fatigue; oversizing wastes fuel and money.
This tool inflates your running and peak targets by a planning margin, then selects the smallest illustrative tier from a table of common running/surge pairs.
Altitude, temperature, fuel type, THD-sensitive electronics, transfer switches, and NEC or local transfer equipment rules are not modeled.
Always follow manufacturer data sheets, startup sequences, and professional engineering for standby, grid-tie, or life-safety loads.
How sizing works here
Requirements with margin
Required running = (total running watts) × (1 + margin%). Required surge = max(required running, peak watts × (1 + margin%)) when peak is supplied; otherwise peak defaults to running.
We then pick the first catalog-style tier where rated running ≥ required running and rated surge ≥ required surge.
kVA hint
If power factor PF is set: approximate kVA ≈ (required surge watts) ÷ (1000 × PF). Generators are often marketed in watts or kW; kVA matters for heavily reactive loads.
Illustrative tiers (running / surge W)
| Typical use | Run | Surge | Tier (W) | Note |
|---|---|---|---|---|
| Camping / minimal | 1,000 | 1,200 | 1k / 1.2k | Lights, small chargers |
| RV / small tools | 3,600 | 4,500 | 3.6k / 4.5k | Single small motor |
| Home essentials | 7,500 | 9,375 | 7.5k / 9.4k | Fridge + furnace fan + some lights |
| Larger backup | 12,000 | 15,000 | 12k / 15k | Multiple motor loads — verify peaks |
Examples
Mostly resistive — 2,400 W running
Leave peak blank with 15% headroom → required ≈ 2,760 W run and surge. Often lands near a 3 kW class tier.
Well pump + household
Running 5,000 W but 9,000 W simultaneous peak → surge drives the tier; headroom applies to both numbers.
Job-site
Add all tools that run together, then add the worst motor start increment your vendor documents — treat that as peak.
When in doubt
Round up tier, verify with transfer equipment ampacity, and follow NEC Article 702 / local rules for standby.
FAQ
Retail SKUs differ by region and year. We use generic tiers; cross-check nameplate running and starting watts.
A common rule is: sum running watts, then add (largest motor surge − that motor’s running watts). You can approximate by setting peak to your computed worst-case simultaneous watts.
This page is watt-based and phase-agnostic. Three-phase kW/kVA projects need manufacturer and engineer involvement.
Use our Electrical calculators, Circuit Breaker Size, and Wire / Cable Size tools after you firm up steady-state and circuit-level planning.