Fuel Injector Size Calculator with transparent formulas, clear units, and instant results. Estimated injector flow: Q = hp × BSFC ÷ (N × d).
Stable formula
This calculator uses a stable mathematical formula. Always verify the values you enter.
Accuracy level
High when inputs and units are correct.
Last reviewed
July 9, 2026
Formula or source
Stable mathematical formula explained on the page.
Guide reading time
4 min
Confidence
High for the stated calculation.
Result type
Formula result, not an official certification.
Do not use for: Cases with missing data, unclear units, or a required professional certification.
How Fuel Injector Size Calculator works
The Fuel Injector Size Calculator uses these inputs: Target power (hp), BSFC (lb/hp/hr), Number of injectors, Duty cycle (%). Its primary output is Estimated injector flow. Performance tools use theoretical relationships between power, RPM, gearing, and engine geometry.
The engine implements Q = hp × BSFC ÷ (N × d). Validation runs first to reject zero divisors and non-finite values.
Numeric example using the starting values: Fuel Injector Size Calculator: Target power (hp): 300 · BSFC (lb/hp/hr): 0.5 · Number of injectors: 4 · Duty cycle (%): 80. The resulting output is Estimated injector flow: 492.19 cc/min.
Fuel Injector Size Calculator: This result is a calculation estimate only. It does not approve installation, safety, legality, or vehicle fitment. Verify it with the vehicle manufacturer, a qualified professional, and local law. Drivetrain loss, traction, air conditions, calibration, and mechanical condition are excluded unless entered.
💡 Useful Tips
Do not mix units between Target power (hp) and BSFC (lb/hp/hr); make sure both describe the same scenario. Use the result for engineering comparison, not as a performance guarantee or tuning instruction.
Do not treat Fuel Injector Size Calculator — Estimated injector flow as mechanical, safety, legal, or financial approval.
Frequently Asked Questions
What does Estimated injector flow mean?
It is the direct output of the formula and entered values, and applies only to the defined scenario.
Which inputs change the result?
The active inputs are Target power (hp), BSFC (lb/hp/hr), Number of injectors, Duty cycle (%). Changing any one runs the same formula again. A theoretical result does not replace dyno measurement or professional inspection.
What to check next
The result is a starting point. For a clearer picture, continue to a related calculator or read a short guide that explains the assumptions.