About this tool
The Fuel Injector Size Calculator sizes injectors for a build. Total fuel demand in lb/hr equals target crank horsepower × BSFC (brake specific fuel consumption), and dividing that by the number of injectors and the maximum duty cycle gives the flow each injector must deliver: per-injector lb/hr = (HP × BSFC) / (injectors × duty). Flow is also shown in cc/min using the gasoline conversion cc/min ≈ lb/hr × 10.5.
BSFC is the key assumption. Naturally aspirated gasoline engines typically run about 0.45–0.50 lb/hp/hr, while forced-induction (turbo/supercharged) setups run richer at roughly 0.55–0.65. Duty cycle is capped — 80% is the usual safe ceiling so injectors are not run wide-open and keep some headroom and cooling. Enter your HP goal, cylinder/injector count, BSFC and duty and the tool returns the required flow per injector plus total fuel demand.
A reverse mode goes the other way: enter a known injector flow (in cc/min or lb/hr) and it reports the maximum crank horsepower that set of injectors can support, HP = (flow × injectors × duty) / BSFC. This is ideal for checking whether injectors you already own are big enough, or how much margin you have. All math runs locally in your browser; treat the results as a sizing estimate and verify with proper tuning on a dyno.