What size generator does a food truck need?
Most food trucks need a generator rated for 3,500 to 7,000 running watts. A truck that cooks on propane and only powers refrigeration, lights, a POS, and a vent fan usually lands at 3,500–5,000 W. Electric griddles or fryers push that to 8,000 W and up, and working at elevation raises it further. The exact number depends on what’s on your truck, which is what the calculator above works out from your own equipment.
How to size a food truck generator
Sizing comes down to a few numbers. Get them right and you buy once instead of twice.
- Running watts — everything that’s on at the same time, added up. Your steady draw during service.
- Starting (surge) watts — the brief spike when a motor kicks on. A refrigeration compressor can pull several times its running watts for a moment.
- Headroom — you don’t run a generator flat out for hours. The rule of thumb is that your typical draw should sit around 80% of the rating. But your typical draw is well under the everything-on total, because fridges, freezers, and thermostat-controlled heat all cycle. So the tool checks both: the unit has to carry the everything-on moment with a little to spare, and its typical hour has to stay under 80%. Whichever needs the bigger generator wins — and it’s usually the first.
- Altitude and heat — a generator makes less power the higher and hotter you work. At 5,000 feet you can be down close to a fifth of the output on the box.
Running watts vs. starting watts
This is the part that catches people. A fridge might say 700 watts on the label, but the instant its compressor cycles on it can yank several times that for a heartbeat. If the generator can’t cover the spike it browns out or trips — usually mid-rush, never while you’re testing in the driveway.
Most heating gear is different. A griddle, fryer, toaster, or coffee brewer is mostly a resistance element, so it draws about the same starting as running. That’s why this tool only stacks a surge onto motor-driven equipment: compressors, fans, pumps, and blenders. Watch for heating equipment that also contains a blower or pump, though — then it surges too.
The largest-surge rule. You size for your running total plus the single biggest startup surge, not every surge added together. Everything in a truck is switched on at once in practice, but the compressors don’t start together — each one is on its own thermostat, an inrush is over in a second or two, and plenty of commercial refrigeration has a built-in delay to stop it short-cycling. Sizing for two spikes landing in the same instant means buying a much bigger generator to insure against a brief flicker, which nobody does. The one time it genuinely happens is a cold start with every box warm, and the fix there is free: switch your refrigeration on one unit at a time and let each compressor settle before the next.
Altitude changes the answer
Small engines breathe thinner air as you climb, and output falls with them. Manufacturer figures vary, but a common published rule is roughly 3.5% less power per 1,000 feet of elevation, plus about another 1% for every 10°F above 77°F. Work a mountain town at 7,000 feet on a 95°F afternoon and a generator can be giving up around a quarter of what the box promises.
That’s why elevation is a field in this calculator and not a footnote. Check your specific generator’s manual for its own derating figure before you buy — some engines also need a high-altitude carburetor jet to run right up there.
Propane vs. electric changes everything
The biggest lever on generator size isn’t how much you cook, it’s what you cook with. A truck that cooks on propane and only needs power for a fridge, lights, a POS, and a vent fan runs happily on 3,500–5,000 watts. Move that cooking to electric griddles and fryers and you’re looking at 10,000–15,000 watts and a much bigger, thirstier unit. If it burns propane, leave it out here — though do count any electric ignition, controls, or blower it has.
120V, 240V, and why total watts isn’t the whole story
Most trucks run mostly 120-volt gear with a few 240-volt heavy hitters — large electric fryers and griddles, tank water heaters, some mini-split HVAC. Rooftop A/C on a truck or RV is usually 120V, so don’t assume it’s the 240V load.
Here’s the trap: a 120/240V generator splits its capacity across two 120-volt legs. You can sit comfortably under its total watt rating and still overload one leg. A 7,200-watt unit gives you roughly 30 amps per leg; pile 4,000 watts of 120V equipment onto one side and 1,000 on the other and that first leg is over its limit while the total looks fine. Spread your 120V circuits across both legs, and check the per-leg amp rating, not just the headline watts.
How to read your equipment’s nameplate
Every piece of gear has a label, usually on the back or inside the door. Here’s what to do with it:
- If it lists watts, use that number directly.
- If it lists only volts and amps, multiplying them gives you VA (apparent power), not true watts. For heating elements the two are nearly identical. For motors, true watts are lower — so using volts × amps is a safe, slightly conservative number for sizing.
- For fridges, freezers, A/C, and pumps, look for starting amps, LRA (locked rotor amps), or a starting-watts figure. That’s your surge number, and it’s often far higher than the running figure.
- Nameplate beats any preset in this tool. The values here are typical figures to get you in the right range — every field is editable, so overwrite them with your own.
Generator safety. This calculator estimates electrical capacity only. It says nothing about safe placement, ventilation, exhaust routing, fuel systems, wiring, grounding and bonding, breaker sizing, or code compliance. Portable generators produce carbon monoxide and are meant to run outdoors, away from doors, windows, and anywhere people are working — never inside an enclosed compartment. Permanently installed vehicle generators are a different category with their own installation requirements. Follow the manufacturer’s instructions and your local codes, and get an electrician involved for anything hard-wired or 240V.
What size generator do I need for a food truck?
Most trucks land between 3,500 and 12,000 watts. Cook on propane and only power refrigeration, lights, and a POS, and a 3,500–5,000W inverter is often plenty. Cook on electric griddles or fryers and you’re usually in the 8,000–15,000W range. Add your actual equipment above for a number matched to your setup and your elevation. If you’ve metered your truck, compare the meter to the “typical draw” figure in the results, not the everything-on total — the meter reads the average while compressors cycle.
What’s the difference between running and starting watts?
Running watts is the steady power a device uses while it’s on. Starting watts is the brief spike when a motor first turns on — compressors and pumps can pull several times their running watts for a second or two. Generators are sold with both numbers, and the starting figure is usually the bigger one on the box.
Is the number on the front of the box the running watts?
Usually not. Generators are typically marketed with their peak or starting rating, while the continuous running rating is lower — a unit sold as 4,500 watts may only be rated for 3,500 running watts. That’s why this calculator gives you both numbers to shop against, so you can check the spec sheet rather than the sticker.
Does altitude really matter that much?
Yes, more than most people expect. A common published figure is around 3.5% power loss per 1,000 feet, plus roughly 1% per 10°F above 77°F. At 5,000 feet on a hot day that can be a fifth of your output gone. Derating varies by engine, so check the manual for your specific unit — and ask whether it needs a high-altitude jet.
Why size to 80% instead of the exact number?
Running a generator near 100% for hours wears it out faster, burns more fuel, and leaves no margin. The 80% rule applies to your typical draw — what a meter shows during service, with compressors and thermostats cycling — not to the brief moment when everything happens to be on at once. This calculator estimates both. It sizes so the unit carries the everything-on moment with 10% to spare and so your typical hour stays under 80%, and whichever needs the bigger generator sets the number. Sizing to the everything-on moment usually satisfies the 80% rule by itself, which is why the two don’t get stacked on top of each other.
Do I need an inverter generator?
Not necessarily, but they generally produce cleaner power with much lower harmonic distortion, and they’re usually quieter and more fuel-efficient at partial load. If your truck runs POS terminals, kitchen display tablets, or refrigeration with electronic controls, check whether any of that equipment specifies a distortion limit before you buy a conventional unit.
Does propane fuel change the generator’s output?
Usually a little. Many dual-fuel generators are rated lower on propane than gasoline — often around 10% less, though it’s model-specific. If you plan to run propane, size against the propane rating on the spec sheet, not the gasoline number on the front of the box. Propane’s advantage is that it doesn’t go stale the way gasoline does.
Does propane cooking equipment count toward generator size?
Mostly no. If a griddle, fryer, or range burns propane it doesn’t draw cooking power from the generator, so leave it out. Do count any electric parts it has — ignition, control boards, and especially any blower or pump, which can surge like any other motor.
Can one generator run my whole truck?
Usually yes, if you size for the running total plus your largest startup surge and stage your motors on. The exception is all-electric cooking — multiple griddles and fryers can exceed what a single portable unit handles, and some operators split loads or move up to a towable or permanently installed unit.
Estimates use standard generator sizing practice: the total of everything running at once plus the largest expected motor surge, with a 10% margin on that peak and a separate check that the typical draw (each appliance weighted by how much of the time it actually runs) stays under 80% of rated continuous output, then adjusted for elevation and temperature using a common published derating rule of about 3.5% per 1,000 feet and 1% per 10°F above 77°F. Real derating, duty cycles, surge behavior, and equipment draw vary by manufacturer and model. Confirm against your equipment’s nameplate ratings and your generator’s specification sheet, and consult a licensed electrician before purchasing or wiring anything.