Speeds & Feeds Calculator (Milling/Drilling)
Enter your tool and cutting data to calculate spindle RPM, feed rate, and optional material removal rate (MRR). This is designed as a practical starting-point calculator for CNC and manual machining.
Preset values are conservative starting points. Adjust for tool coating, machine rigidity, runout, coolant, and cutter engagement.
What are cutting speed and feed rate?
In machining, cutting speed is how fast the cutting edge moves across the material surface, and feed rate is how fast the tool advances through the work. These are two of the most important parameters for tool life, surface finish, cycle time, and part accuracy.
If your speed is too high or your feed is too low, you can rub instead of cut. If feed is too high for the setup, you can overload the tool, increase chatter, or snap cutters. The best settings are always a balance between material, tool geometry, machine capability, and operation type.
Core formulas used in this calculator
Spindle Speed (RPM)
Imperial: RPM = (SFM × 12) / (π × Tool Diameter in inches)
Metric: RPM = (Vc × 1000) / (π × Tool Diameter in mm)
Feed Rate
Feed per minute = RPM × Number of Flutes × Chip Load per tooth
In imperial units this gives IPM (inches/minute). In metric it gives mm/min.
Material Removal Rate (optional)
With axial and radial engagement entered, this tool also estimates MRR:
MRR = Feed × DOC × WOC.
How to use this calculator effectively
- Pick a unit system first (imperial or metric).
- Choose a material preset or enter your own cutting speed and chip load.
- Enter tool diameter and flute count.
- Add max spindle RPM if your machine has a hard limit.
- Optionally enter DOC and WOC to estimate MRR.
- Run a test cut and tune from sound, chip shape, spindle load, and finish.
Typical starting ranges (carbide tools)
| Material | Speed (SFM) | Speed (m/min) | Chip Load (in/tooth) | Chip Load (mm/tooth) |
|---|---|---|---|---|
| Aluminum | 600–1200 | 180–365 | 0.002–0.006 | 0.05–0.15 |
| Mild Steel | 250–500 | 75–150 | 0.0015–0.004 | 0.04–0.10 |
| Stainless | 150–350 | 45–105 | 0.001–0.003 | 0.025–0.08 |
| Titanium | 80–200 | 25–60 | 0.0008–0.0025 | 0.02–0.06 |
Common mistakes to avoid
1) Ignoring machine limits
A small tool in aluminum may call for very high RPM. If your spindle cannot reach it, use the max RPM and recalculate feed from chip load, not guesswork.
2) Using one chip load for every tool size
Chip load scales with cutter diameter, flute length, and rigidity. A 1/8" end mill does not run the same chip load as a 1/2" rougher.
3) Forgetting tool engagement effects
Full-slotting, adaptive clearing, and light finishing passes all behave differently. Radial engagement changes chip thickness, heat, and force.
4) Chasing finish with very low feed
Extremely low feed often causes rubbing and heat. Better finish usually comes from balanced speed/feed, stable setup, and sharp tooling.
Practical tuning workflow
- Start conservative from tool manufacturer data or this calculator.
- Watch chips: color, shape, and consistency matter.
- Listen for chatter and monitor spindle load.
- Increase feed before speed when chips are too thin.
- Reduce speed or engagement if heat and wear rise quickly.
Final note
This calculator is a strong baseline for milling and drilling setups, but real-world performance depends on fixture rigidity, stick-out, coolant strategy, machine condition, and cutter quality. Use it as the starting point, then dial in your process with data from test cuts.