Fuel Injector Size Calculator - Calculate Injector Sizing for Your Engine
Fuel Injector Sizing Calculator
Use this fuel injector sizing calculator to convert your target horsepower into a recommended injector size. Enter a few basics and get a clear injector flow rate in lb/hr and cc/min. It works with common fuels and injection setups, helping you choose a safe, realistic size with headroom for tuning and confirm whether your current injectors can meet your power goals.
Prefer a walk through? Read how to choose injectors and the E85 fuel guide.
Engine Configuration
Basic Configuration
Engine & Fuel Type
Injection System
Advanced Settings
Typical range: 70-80%. Lower for direct injection.
Default: 43.5 psi (standard rating)
This tool provides estimates for informational purposes only. Results depend on your inputs and assumptions. It is not a substitute for manufacturer data, professional calibration, or safety checks. You are responsible for verifying injector choice, duty cycle, pressure, and compliance. TIRES + TERRAIN accepts no liability for loss, damage, or injury from use of this tool.
Quick Guide
Target Horsepower
Maximum power you expect to produce at peak conditions
Duty Cycle
Percentage of time injectors are open. Stay under 85% for reliability
Fuel Pressure
Most injectors rated at 43.5 psi. Adjust only if using different base pressure
Common Sizes
Fuel Injector Sizing FAQs
What duty cycle should I target?
For port injection 70 to 80% is typical. For direct injection aim lower, about 65 to 70%.
Why are injectors rated at 43.5 psi?
43.5 psi is 3 bar, a common reference. Flow scales roughly with the square root of pressure.
How does E85 change sizing?
E85 needs more fuel mass per horsepower, so use a higher BSFC than petrol. Read E85 fuel guide for more info.