Power & Electrical calculator
Generator Size Calculator for Events
Size a show generator by summing the real connected load in kW, dividing by your target loading (diesel generators run best between 50% and 80% of rating), and converting to kVA at the system power factor. This calculator does that math and suggests the smallest standard rental class that covers it.
Catering, comms, chargers, office power, HVAC. It adds up faster than departments admit.
Generator nameplates are kVA at 0.8 PF; modern PFC loads run closer to 0.95.
Diesel gensets like 50 to 80% load: headroom for inrush, without wet-stacking at idle.
Formulas
Required capacity
kW(required) = kW(load) / (loading% / 100)- kW(load):
- total connected load in kilowatts
- loading%:
- target maximum loading, typically 80%
kVA from kW
kVA = kW / PF- PF:
- power factor of the combined load
Generator nameplate constraint
required class (kW) = max(required kW, required kVA × 0.8)- 0.8:
- the rated power factor used for common generator kW/kVA nameplates
How it works
Generators are rated in kVA (apparent power) at an assumed 0.8 power factor, while show loads are usually discussed in kW (real power). The power factor bridges the two: a 100 kVA set delivers 80 kW at 0.8 PF. Modern power-factor-corrected amplifier and LED loads run closer to 0.9 to 1.0, which effectively buys back capacity.
The loading target matters in both directions. Oversized diesels running at 10 to 20% load for hours suffer wet stacking (unburned fuel fouling the exhaust), while a set near 100% has no headroom for chain motor inrush, amplifier transients, or the coffee urn nobody declared. 50 to 80% loading is the standard guidance.
Sum realistic loads, not nameplate worst cases: amplifier racks at one-eighth power for music, LED walls at typical content brightness (full-white peak only for safety margin), moving lights at lamp-on plus motors. Then let the loading target provide the safety factor once, rather than stacking hidden margins at every step.
Worked example: Festival side stage: 12 kW audio, 20 kW lighting, 15 kW video, 8 kW other
- 1.Connected load: 12 + 20 + 15 + 8 = 55 kW.
- 2.At 80% max loading: 55 / 0.8 = 68.75 kW required.
- 3.In kVA at 0.8 PF: 68.75 / 0.8 = 85.9 kVA. The smallest standard class above 68.75 kW is a 100 kW set.
Spec a 100 kW (125 kVA class) generator; it runs at a healthy 55% load.
Rough department draws for early planning
| Department | Small show | Mid-size show |
|---|---|---|
| PA + monitors + amps | 5-10 kW | 15-40 kW |
| Lighting (LED-heavy rig) | 5-15 kW | 20-60 kW |
| LED wall (per 100 sq ft, typical content) | 3-6 kW | 3-6 kW |
| Backline + stage power | 2-4 kW | 4-8 kW |
| Production/catering/other | 3-8 kW | 10-25 kW |
Field notes
- Ask every department for amps at voltage, not "watts"; convert yourself. Answers arrive in mixed units and optimistic memories.
- Chain motor inrush is brutal but brief: a dozen 1 hp motors starting together can momentarily demand several times their running load. Stagger the pickups.
- Verify the rental fleet sizes; the ladder in this tool reflects common classes, but every regional supplier stocks differently.
Frequently asked questions
What size generator do I need for a stage and PA?
Sum the real kW draw of every department, divide by 0.8 for loading headroom, and rent the next standard size up. A small club-level rig often fits a 20 to 45 kW set; a festival stage with LED video typically lands at 100 kW and up.
What is the difference between kW and kVA on a generator?
kVA is apparent power, kW is real power: kW = kVA × power factor. Generator nameplates assume 0.8 PF, so a 100 kVA set is an 80 kW set for planning purposes.
Is it bad to run a generator at low load?
For diesels, yes, over long periods: light loading causes wet stacking and fouling. Rental guidance is to keep sustained load above roughly 30 to 50% of rating, which argues against reflexively oversizing.
Should I get one big generator or two smaller ones?
Shows that cannot go dark often run paired sets with a transfer switch, or a dedicated quiet set for audio to isolate it from motor and dimmer noise. Redundancy is a production decision, not a math output.