Speed Calculator

Calculate RPM, surface speed, or diameter for rotating objects. Convert between linear and rotational speed for machining, wheels, pulleys, and rotating machinery.

How It Works

What is Surface Speed?

Surface speed (also called cutting speed, peripheral speed, or linear speed) is the speed at which the outer edge of a rotating object moves. It depends on both the rotational speed (RPM) and the diameter of the object. A larger diameter at the same RPM produces a higher surface speed.

Key Formulas

• V = π × D × n — surface speed from diameter and RPM
• n = V / (π × D) — RPM from surface speed and diameter
• D = V / (π × n) — diameter from surface speed and RPM
• ω = 2πn / 60 — angular velocity (rad/s) from RPM
• V = ω × r — surface speed from angular velocity and radius

Common Speed Units

Practical Examples

• A 100 mm diameter end mill at 1500 RPM has a surface speed of 471 m/min
• To achieve 200 SFM on a 2-inch lathe workpiece, set the spindle to about 382 RPM
• A car tire (diameter 660 mm) at 60 km/h rotates at about 482 RPM
• A grinding wheel (300 mm) typically runs at 25–35 m/s surface speed for safety

Machining Applications

In CNC machining and manual turning/milling, the correct surface speed is critical for tool life and surface finish. Each material and tool combination has a recommended cutting speed range (usually in m/min or SFM). The machinist then calculates the required spindle RPM based on the tool or workpiece diameter. Too slow wastes time; too fast causes excessive tool wear or workpiece damage.

Related Utils

• Torque Calculator — calculate torque, force, and rotational power
• Gear Ratio Calculator — calculate gear ratios, speed, and torque
• Belt Length Calculator — calculate belt lengths for pulley systems
• Velocity Calculator — calculate linear velocity and acceleration
• Unit Converter — convert between engineering units