Jump Starter Size Calculator
Enter your engine's displacement and fuel, and tick what applies: cold winters, a vehicle that sits, or a two-battery diesel. The calculator gives the engine rating to look for on the box, which is the 'up to X.0L gas / Y.0L diesel' line makers print, not the peak-amp headline, plus a comfortable step up and a reference class from a common brand ladder. Already own a pack? Enter its rating to see if it is enough. The rule is our editorial sizing method built on makers' published ratings; your pack's manual governs. Everything runs in your browser; nothing is uploaded or stored.
Find displacement in the owner's manual specifications, on the emissions label under the hood, or on the badge (for example "5.3L V8" or "6.7 Turbo Diesel"). 12V vehicles only.
Calculating...
How it works
Engine rating, not peak amps. Every reputable jump starter maker prints an engine rating such as "up to 6.0L gas / 3.0L diesel". That figure is comparable across brands; peak amps are not, because no single test method is used to state them. The calculator works entirely in engine ratings.
The rule. Find the smallest common rating that covers your displacement on your fuel's line, then add one step of headroom if any of the boxes are ticked. The steps are the ratings in a common maker ladder: 3, 6, 7, 8, 9 and 10 liters for gas, and 3, 4.5, 6, 7 and 10 liters for diesel. The "comfortable" figure is one further step, for a pack with reserve for a very flat battery or extra starts.
Reference classes. The NOCO GB40, GB50, GB70 and GB150 and the GOOLOO GP4000 are listed as 6/3, 7/4.5, 8/6, 9/7 liters gas/diesel and all gas/10 liters diesel respectively, per their listings checked 2026-10-28. They are shown only as a familiar yardstick; any brand with the same engine rating on the same fuel line is equivalent on paper.
What it does not cover
- 24V trucks and equipment, which need a 24V-rated pack; see best 24V jump starter.
- Batteries that are completely flat or damaged, which may need the pack's override or boost mode, or a charger rather than a jump; see how to use a jump starter.
- Exact cold-weather derating. No maker publishes output by temperature, so the cold box adds one step rather than a calculated figure.
- Starts per charge and size. A bigger pack stores more starts but may not fit the glove box; the best pack is the one that stays in the car.
An editorial sizing rule built on published ratings, not a manufacturer chart. Confirm the engine rating on the box and follow your pack's manual. See the disclosure page for the site's relationships.
Data last verified 2026-11-09. Prices, hours and rules change; results are estimates from what you enter; the manufacturer label and manual govern.
Sources
Related guides
Frequently asked questions
What size jump starter do I need for my car?
Pick a pack whose published engine rating for your fuel covers your engine displacement, then add one step of headroom if you have cold winters or the car sits for long stretches. A 2.0L gas car is covered by a 3L-gas pack; a 5.3L V8 in a cold state wants at least a 7L-gas pack.
Why not just compare peak amps?
Peak amps are a brief maximum with no single industry test method, so the number only compares packs within one brand. Two packs both sold as 4000A can differ by four liters of diesel rating. The engine rating ("up to 6.0L gas / 3.0L diesel") is the figure makers print that you can compare across brands.
Why is the diesel rating lower than the gas rating?
Diesels run much higher compression, often use glow plugs or intake heaters that draw current while cranking, and many pickups carry two batteries. Every maker rates its packs for a smaller diesel than gas engine, so always read the diesel line for a diesel.
How much bigger should I buy for cold weather?
One step up the ladder. In the cold the dead battery delivers less current, the engine is harder to turn, and the lithium pack is weaker too. No maker publishes an exact output drop by temperature, so the simple rule is one rung of headroom for regular sub-freezing winters.
Will a 12V jump starter start a 24V truck?
No. Heavy trucks and some equipment run 24V systems and need a pack specifically rated for 24V. This calculator covers 12V vehicles only.