Fuel injector flow rate calculator

Required flow per injector = horsepower × fuel consumption ÷ injector count ÷ duty-cycle fraction.

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Engine power (horsepower)

Fuel consumption (lb per horsepower-hour)

More inputs and assumptions

Injector count

Maximum duty cycle (%)

Answer

…

Required flow per injector = horsepower × fuel consumption ÷ injector count ÷ duty-cycle fraction.

More results

Precision and calculation record

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Formula and assumptions

Uses your brake-specific fuel consumption and duty-cycle assumptions. Output is mass flow per injector at the operating conditions used for those assumptions. Fuel density, pressure changes, transient enrichment and fitment are not inferred.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-29

Using Fuel injector flow rate calculator

Required flow per injector = horsepower × fuel consumption ÷ injector count ÷ duty-cycle fraction.

Next: Engine horsepower calculator

A worked example

For engine power (horsepower) = 400, fuel consumption (lb per horsepower-hour) = 0.5, injector count = 8, maximum duty cycle (%) = 80, flow per injector (lb/hour) = 31.25.

Before you use the result

Example results for engine power (horsepower)

These examples use Fuel consumption (lb per horsepower-hour): 0.5; Injector count: 8; Maximum duty cycle (%): 80. They are reference calculations, not recommended settings.

Engine power (horsepower)	Flow per injector (lb/hour)
200	15.625
400	31.25
800	62.5

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ToolOctopus. “Fuel injector flow rate calculator.” Updated 2026-09-29. https://tooloctopus.com/fuel-injector-flow-rate-calculator.

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