RPM Calculator
Calculate engine RPM, vehicle speed, transmission ratios, and wheel rotations
RPM & Speed Calculator
What do you want to calculate?
Revolutions per minute of the engine
Revolutions per minute of the wheels
Overall drivetrain gear ratio
Overall diameter of the tire
Calculation Results
Tire Information
Key Formulas
Quick Reference
Common Ratios
1st Gear
3.5:1 to 5:1 ratio
2nd Gear
2:1 to 3:1 ratio
3rd Gear
1.5:1 to 2:1 ratio
4th/5th Gear
0.8:1 to 1.2:1 ratio
Final Drive
3:1 to 5:1 ratio
Understanding RPM
What is RPM?
RPM stands for Revolutions Per Minute. It measures how many complete rotations an object makes in one minute. In automotive applications, it typically refers to engine crankshaft speed.
Key Relationships
Engine to Wheels:
Engine RPM = Wheel RPM × Transmission Ratio
Wheels to Speed:
Speed = Wheel RPM × Tire Diameter × π × 60 ÷ 63360
Why RPM Matters
- •Engine efficiency and power output
- •Fuel consumption optimization
- •Transmission gear selection
- •Engine longevity and maintenance
Transmission Systems
Manual Transmission
Fixed gear ratios selected by the driver. Lower gears provide more torque multiplication for acceleration, higher gears provide better fuel economy.
Automatic Transmission
Variable gear ratios selected automatically based on speed, throttle, and other factors. May include a torque converter that provides additional multiplication.
CVT (Continuously Variable)
Infinite gear ratios within a range. Can maintain optimal engine RPM for any driving condition, maximizing efficiency and performance.
Frequently Asked Questions
What's the ideal RPM for fuel economy?
Most engines are most efficient between 1500-2500 RPM. This is typically achieved in higher gears at moderate speeds. Driving in this range maximizes fuel economy.
How does tire size affect RPM?
Larger tires reduce RPM for a given speed because they cover more ground per revolution. Smaller tires increase RPM. This affects speedometer accuracy and fuel economy.
What happens at high RPM?
High RPM increases engine wear, heat, and stress. Most engines have a "redline" RPM limit to prevent damage. Modern engines have rev limiters to protect against over-revving.