Drill Speed Calculator
Enter fractional (1/4"), number (#30), or letter (A) drill size
Diameter in inches (e.g. 0.25 for 1/4")
Surface Feet per Minute — auto-filled from material preset, editable
Inches per revolution — auto-suggested from diameter
Typically 2 for standard twist drills
Required for cut time calculation
Enter Drilling Parameters
Select your work material, drill bit type, and diameter to see RPM, feed rate, chip load, and cut time recommendations.
How to Use the Drill Speed Calculator
Select Unit System and Material
Choose Imperial (inches, SFM) or Metric (mm, m/min) based on your working units. Then select your work material from the dropdown — the calculator automatically fills in the recommended surface speed (SFM or m/min) for that material based on published machining tables.
Set Drill Bit Type and Diameter
Select your drill bit material (HSS, Cobalt, TiN, TiAlN, or Carbide). This applies the correct SFM multiplier over the HSS baseline. Enter the drill diameter directly, or use the Drill Size Lookup to convert a fractional size (1/4"), letter drill (A–Z), or number drill (#1–#80) to its decimal equivalent, which populates the diameter field automatically.
Adjust Feed and Flutes
The feed per revolution (IPR or mm/rev) is auto-suggested based on your drill diameter using standard reference tables. You can override this value. Enter the number of flutes (default 2 for standard twist drills). Optionally enter hole depth to calculate cut time using the Norseman feed stroke method (depth plus one-third of drill diameter for the drill point).
Read Results and Find Nearest Machine Speed
Review your computed RPM, feed rate, chip load per tooth (IPT), and cut time. The Machine Speed Guide shows where your RPM falls among the standard drill press speed steps (250, 500, 750, 1000, 1500, 2000, 3000 RPM), highlights the nearest available step, and warns you if your RPM exceeds 3000. Export the results to CSV or print them for your shop documentation.
Frequently Asked Questions
What is the formula for calculating drill RPM?
The RPM formula for imperial units is: RPM = (SFM × 3.82) / Diameter in inches. The constant 3.82 is derived from 12 divided by π (pi). For metric units: RPM = (SMM × 318.3) / Diameter in millimeters, where 318.3 comes from 1000 divided by π. SFM is the Surface Feet per Minute recommended for your work material and drill bit type. For example, drilling aluminum (SFM 250) with a 1/2-inch HSS drill gives RPM = (250 × 3.82) / 0.5 = 1910 RPM. Larger diameters require lower RPM to maintain the same surface speed. This is why a 2-inch hole saw runs much slower than a 1/8-inch twist drill in the same material.
What SFM should I use for different materials?
SFM values vary widely by material hardness and thermal conductivity. Common HSS twist drill SFM values include: Aluminum 200–300 SFM, Brass 150–200 SFM, Mild Steel 100–150 SFM, Cast Iron (gray) 100–150 SFM, Stainless Steel 25–40 SFM, Titanium 20–40 SFM, Hardened Steel 40–60 SFM, Wood/MDF 300–600 SFM, and Plastics 150–200 SFM. Carbide drill bits can run 2–3 times faster than HSS in most materials. Always start at the conservative (low) end of the range and increase if tool life and chip color are acceptable. Blue or brown chips from steel indicate too much heat — reduce SFM.
How do I choose the right feed rate (IPR)?
Feed per revolution (IPR) depends primarily on drill diameter, not material. Larger drills can take heavier chips. Standard recommendations: drills under 1/8-inch should feed at 0.001–0.003 IPR; 1/8" to 1/4" drills use 0.002–0.006 IPR; 1/4" to 1/2" drills use 0.004–0.010 IPR; 1/2" to 1" drills use 0.007–0.015 IPR; drills over 1" use 0.010–0.025 IPR. Feeding too lightly causes the drill to rub rather than cut, generating heat and dulling the drill. Feeding too aggressively risks drill breakage. This calculator auto-suggests the mid-range IPR for your diameter and displays the low and high bounds as guidance.
Why does my RPM exceed 3000 and is that dangerous?
Small-diameter drills in soft materials commonly require RPM above 3000. For example, a 1/16-inch drill in aluminum at 250 SFM computes to about 19,100 RPM — far beyond a typical benchtop drill press. The 3000 RPM warning in this calculator flags values that exceed the typical maximum speed of a consumer drill press (which usually tops out at 3000–3500 RPM). If your computed RPM exceeds your machine's maximum, either reduce SFM toward the low end of the range, use a slower-SFM material preset, or accept that you must run below optimal speed. CNC machining centers and high-speed spindles can safely exceed 10,000 RPM — the warning is for drill press users only.
What is chip load per tooth (IPT) and why does it matter?
Chip Load per Tooth (IPT) is the thickness of the chip each flute removes per revolution. It equals the feed per revolution (IPR) divided by the number of flutes. For a 2-flute drill at 0.006 IPR, IPT = 0.003 inches per tooth. Chip load directly affects surface finish, heat generation, and tool life. Too low a chip load causes rubbing, heat, and rapid dulling. Too high a chip load overloads the cutting edge and may break the drill. IPT is most useful when switching between drills with different flute counts or when you want to match the chip load to a known material recommendation from a tool manufacturer's catalog.
How is cut time calculated with the feed stroke method?
Simple cut time divides hole depth by feed rate: Time = Depth / IPM. However, the Norseman feed stroke method — used by professional machinists — adds one-third of the drill diameter to account for the drill point length that protrudes beyond the full-diameter body. The drill point must pass completely through before the hole is finished. Feed Stroke = Hole Depth + (Diameter / 3). Cut Time = Feed Stroke / IPM. For example, drilling a 1-inch deep hole with a 1/2-inch drill at 10 IPM: Feed Stroke = 1.0 + (0.5 / 3) = 1.167 inches. Cut Time = 1.167 / 10 = 0.117 minutes (about 7 seconds). This method provides more accurate cycle time estimates for production planning.