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 minimum required injector flow rate in cc/min and lb/hr. Enter a few basics and get a clear result that works across all fuel types and injection setups, helping you 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 to 80%. Lower for direct injection.
Default: 43.5 psi (standard rating pressure)
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 are rated at 43.5 psi. Adjust only if your base pressure differs
Result
The minimum flow rate your injectors must meet. Choose injectors rated at or above this figure
cc/min to lb/hr Reference
| cc/min | lb/hr |
|---|---|
| 160 | 15 |
| 210 | 20 |
| 260 | 25 |
| 315 | 30 |
| 370 | 35 |
| 420 | 40 |
| 474 | 45 |
| 525 | 50 |
| 630 | 60 |
| 735 | 70 |
| 840 | 80 |
| 945 | 90 |
| 1050 | 100 |
| 1260 | 120 |
| 1575 | 150 |
| 2100 | 200 |
Based on gasoline specific gravity ~0.749 at 43.5 psi
Fuel Injector Sizing FAQs
What duty cycle should I target for fuel injectors?
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 industry reference pressure. Flow scales roughly with the square root of pressure, so if your rail runs higher, your injectors will flow more than their rated figure.
How does E85 change sizing?
E85 needs more fuel mass per horsepower than petrol, so the minimum flow rate will be significantly higher. Read the E85 fuel guide for more detail.
What is the difference between cc/min and lb/hr?
Both measure injector flow rate. cc/min (cubic centimetres per minute) is the metric standard used by most injector manufacturers. lb/hr (pounds per hour) is common in North American tuning. For gasoline at standard conditions, 1 lb/hr is approximately 10.5 cc/min.
How many fuel injectors do I need?
For port injection, use one injector per cylinder. A 4-cylinder engine uses 4 injectors, a 6-cylinder uses 6, and so on. For dual injection setups, you will have one port injector and one direct injector per cylinder.