Injector duty cycle calculator

Duty cycle is the share of the available time an injector spends open. Log a pulse width and an RPM from your ECU or scan tool, enter them here, and see how close to the edge the injectors are running — with a clear warning once you pass the safe zone.

Injector pulse width (ms)

Engine speed (RPM)

For a four-stroke engine each cylinder fires once every two revolutions, which is where the 1200 in the formula comes from.

The formula

Duty cycle % = (pulse width in ms × RPM) ÷ 1200

At any given RPM, the time available for one injection event is fixed. A longer commanded pulse fills more of that window. Cross-check with the time view: at 6,000 RPM one full cycle takes 20 ms, so a 15 ms pulse is open for three quarters of it.

Worked example (pre-filled above): 15 ms × 6,000 RPM ÷ 1200 = 75.0% duty cycle — comfortably inside the safe zone, with a little headroom left.

The safe zone — and past it

Up to 80% — healthy. This is the ceiling good sizing targets; verify with the size calculator.
85–95% — the warning zone. The injector is nearly static, fuel metering goes coarse, and any extra demand (cold weather, a boost spike) has nowhere to go.
100%+ — impossible in practice: the ECU is asking for more time than exists. The injector is simply held open, mixture control is lost, and the real delivered fuel is whatever the injector flows wide open at your rail pressure (check that number). The fix is a larger injector, more pressure, or less power.

Flow is only half the story

A partially clogged micro basket filter cuts real-world flow no matter what the math says. The Micro-Filter Basket Removal Tool, from $14.99, pulls the old ~6 mm basket filter straight out so a fresh one can go in — see the step-by-step removal guide. For a full service, the Universal EV1 Rebuild Kit, $72.49 covers 200 injectors with filters, seals and caps.

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Get the tool — from $14.99 Shop the 200-injector kit — $72.49

More injector calculators

Injector flow converter — cc/min ↔ lb/hr.
Injector size calculator — injector size for a target horsepower.
Max horsepower from your injectors — the reverse calculation.
Flow rate at a different fuel pressure — the square-root rule.
Injector duty cycle calculator — pulse width and RPM to duty %.
Fuel pump flow requirement — LPH your engine actually needs.

Last updated October 20, 2026 · Partsapiens, 5325 Alton Pkwy, Suite C300, Irvine, CA 92604 · partsapiens@gmail.com