Drill Speed Calculator

Disclaimer: While we strive to ensure the accuracy of our calculator tools, we cannot be held responsible for any damages or financial losses resulting from their use.

This Drill Speed Calculator helps you determine the optimal spindle speed (RPM) for your drilling operations based on cutting speed and drill bit diameter. You can quickly calculate the spindle speed by selecting the appropriate units for cutting speed and diameter. This tool is helpful for machinists, engineers, and DIY enthusiasts who need accurate speed settings for different materials and drill sizes.

It also provides an optional SFM (Surface Feet per Minute) input for added flexibility.

How to Calculate Drill Speed (RPM)

Drill speed, measured in Revolutions Per Minute (RPM), is determined using the relationship between cutting speed and drill bit diameter. The formula varies slightly based on the unit system used.

Formula

The general formula to calculate spindle speed (RPM) is:

RPM = (Vc × 1000) π × D

​Where:

• RPM = Spindle speed (Revolutions Per Minute)
• V_c = Cutting speed (meters per minute or feet per minute)
• D = Drill bit diameter (millimeters or inches)
• π (Pi) = 3.1416 (a constant)

Alternative Formula for (SFM)

In the Imperial system, cutting speed is often given in Surface Feet per Minute (SFM), and the formula is:

RPM = (12 × Vc) π × D

Where:

• V_c = Cutting speed in SFM (feet per minute)
• D = Drill bit diameter in inches
• The factor 12 converts feet to inches.

Alternatively, a simplified version is:

RPM = (4 × Vc) / D

Where 4 is an approximation of 12 / π.

Example 1: Using Metric System

A machinist wants to drill a 10 mm hole in mild steel with a recommended 25 m/min cutting speed.

Using the metric formula:

RPM = (25 × 1000) π × 10

RPM = 31.416 × 25000

​RPM = 796

So, the drill should run at 796 RPM.

Example 2: Using Imperial System (SFM)

A machinist is drilling a 0.5-inch hole in aluminum with a recommended cutting speed of 300 SFM.

Using the formula:

RPM = (12 × 300) / 3.14 × 0.5

RPM = 3600​ / 1.57

So, the drill should run at 2292 RPM.

Related Calculator:

Drill tip length calculator

RPM to Speed Calculator