CNC Feeds and Speeds Calculator for Routers
Enter your spindle speed, cutter and material to get a feed rate, or enter a feed you already use to see the chip load it gives.
Your measurements
Enter your cutter, material and spindle speed. Everything updates as you type.
What do you want to know?
Works out the feed from a chip load. The chip load comes from the table or from your own number.
Cutter and material
Common cutters
The cutting diameter of the end mill.
Count the cutting edges (flutes) on the end mill.
Sets the typical starting chip load in the table below.
Spindle
Set it on the router dial or spindle controller. A trim router at its top setting is often around 16,000 to 30,000 RPM; check yours.
Leave at 0 if you are not using it. Enter a surface speed from a cutter maker's chart to get the RPM that gives it.
Chip load
Leave at 0 to use the typical starting value from the table (0.007 in/tooth here). Type your own number from the cutter maker's chart or a test cut.
Plunge
50% is a rule of thumb, not a rule. Change it to suit your cutter and machine.
Results
Feed rate
in/min
= 6,400.8 mm/min
18000 RPM × 2 flutes × 0.007 in per tooth (typical starting value).
- Chip load
- 0.007in/tooth
- Typical starting value
- Surface speed
- 1,178.1SFM
- 359.1 m/min
- Plunge rate
- 126 in/min
- 50% of feed, a rule of thumb
Check before you cut
- Chip loads in the table are typical starting values for a rigid machine, not figures from a cutter maker. Go lower on a hobby CNC and check the cutter maker's chart.
Typical starting chip loads (in per tooth)
Typical starting values for a rigid machine, not figures from a cutter maker. Go lower on a hobby CNC and check the chart for your cutter.
| Material | 0.125 in | 0.25 in | 0.375 in | 0.5 in |
|---|---|---|---|---|
| Softwood / plywood | 0.004 | 0.007 | 0.010 | 0.012 |
| Hardwood | 0.003 | 0.006 | 0.008 | 0.010 |
| MDF | 0.005 | 0.010 | 0.013 | 0.015 |
| Acrylic (cast) | 0.002 | 0.005 | 0.007 | 0.009 |
| HDPE / plastic | 0.004 | 0.008 | 0.011 | 0.014 |
| Aluminium | 0.001 | 0.002 | 0.003 | 0.004 |
The columns are 1/8, 1/4, 3/8 and 1/2 in cutters. Sizes in between are interpolated; outside that range the nearest column is used.
How this was calculated
Surface speed, chip load, feed and plunge, with your numbers.
How this was calculated
Surface speed, chip load, feed and plunge, with your numbers.
Step 1: Surface speed
π × diameter (in) × RPM ÷ 12
= π × 0.25 × 18000 ÷ 12
= 1178.1 SFM (359.1 m/min)How fast the cutting edge moves through the material, in feet per minute. It depends only on the cutter diameter and the spindle speed.
Step 2: Chip load from the table
inches cut by each flute on each turn
= Softwood / plywood, 0.25 in cutter: 0.007 in per tooth
= 0.007 in per tooth (0.1778 mm)A typical starting value for a rigid machine, interpolated between the 1/8, 1/4, 3/8 and 1/2 in columns. Go lower on a hobby CNC and check the cutter maker's chart.
Step 3: Feed rate
RPM × flutes × chip load
= 18000 × 2 × 0.007
= 252 in/min (6400.8 mm/min)The speed the machine moves along the cut. Multiply inches per minute by 25.4 for millimetres per minute.
Step 4: Plunge rate
feed rate × plunge percent
= 252 × 0.5
= 126 in/min (3200.4 mm/min)50% of the feed is a rule of thumb for going straight down. Many cutters plunge slower than they cut sideways; use your own percentage if the cutter maker gives one.
In short
Feed (in/min) = RPM × flutes × chip load. At 18,000 RPM with a 2-flute 1/4 in cutter in softwood / plywood at 0.007 in per tooth, that is 252 in/min (6400.8 mm/min), with a plunge of 126 in/min.
The table values are typical starting values, and you can type your own chip load.
Typical starting chip loads (in per tooth)
Typical starting values for a rigid machine, not figures from a cutter maker. Go lower on a hobby CNC and check the chart for your cutter.
| Material | 0.125 in cutter | 0.25 in cutter | 0.375 in cutter | 0.5 in cutter |
|---|---|---|---|---|
| Softwood / plywood | 0.004 | 0.007 | 0.010 | 0.012 |
| Hardwood | 0.003 | 0.006 | 0.008 | 0.010 |
| MDF | 0.005 | 0.010 | 0.013 | 0.015 |
| Acrylic (cast) | 0.002 | 0.005 | 0.007 | 0.009 |
| HDPE / plastic | 0.004 | 0.008 | 0.011 | 0.014 |
| Aluminium | 0.001 | 0.002 | 0.003 | 0.004 |
Sizes between the columns are interpolated in the calculator. Outside 1/8 to 1/2 in the nearest column is used, so check the maker's chart for very small or large cutters.
Worked example: 1/4 in 2-flute cutter in softwood or plywood
18,000 RPM and the typical starting chip load of 0.007 in per tooth.
Step 1: Surface speed
π × diameter (in) × RPM ÷ 12
= π × 0.25 × 18000 ÷ 12
= 1178.1 SFM (359.1 m/min)How fast the cutting edge moves through the material, in feet per minute. It depends only on the cutter diameter and the spindle speed.
Step 2: Chip load from the table
inches cut by each flute on each turn
= Softwood / plywood, 0.25 in cutter: 0.007 in per tooth
= 0.007 in per tooth (0.1778 mm)A typical starting value for a rigid machine, interpolated between the 1/8, 1/4, 3/8 and 1/2 in columns. Go lower on a hobby CNC and check the cutter maker's chart.
Step 3: Feed rate
RPM × flutes × chip load
= 18000 × 2 × 0.007
= 252 in/min (6400.8 mm/min)The speed the machine moves along the cut. Multiply inches per minute by 25.4 for millimetres per minute.
Step 4: Plunge rate
feed rate × plunge percent
= 252 × 0.5
= 126 in/min (3200.4 mm/min)50% of the feed is a rule of thumb for going straight down. Many cutters plunge slower than they cut sideways; use your own percentage if the cutter maker gives one.
Before you cut
- Check the RPM you set. Many routers have a dial with numbers, not RPM, so look up what each setting means for your model.
- Depth and width of cut matter as much as feed. The chip load here assumes a sensible depth for the cutter, so take shallow passes in hard materials and on light machines.
- Make a test cut in scrap of the same material. Listen, look at the chips and check the edge, then adjust the feed in small steps.
- The cutter maker's chart and your machine's manual come first. This page gives starting points, not limits.
Feeds and speeds: common questions
Chip load, rubbing and hobby machines.
How do you calculate the feed rate for a router?
Multiply the spindle speed in RPM by the number of flutes and by the chip load in inches per tooth. At 18,000 RPM with a 2-flute cutter and 0.007 in per tooth, the feed is 18,000 × 2 × 0.007 = 252 in/min, or about 6,400 mm/min. Multiply inches by 25.4 for millimetres.
What is chip load and where do I get the number?
Chip load is how much material each flute removes on each turn, in inches (or millimetres) per tooth. The best source is the chart from your cutter's maker. The table on this page gives typical starting values for a rigid machine, so use it only when you have no chart, and treat the result as a place to start a test cut.
What does it mean when the cutter is rubbing?
If the chip load is too small, the cutter does not take a real chip. It rubs, makes heat and fine dust, burns wood and melts plastic, and the edge wears faster. The usual fixes are a faster feed or a lower RPM. This tool flags a chip load below about 0.001 in per tooth for wood and plastic, which is a rule of thumb, not a hard limit.
Can I use these numbers on a hobby CNC?
Use them as a ceiling, not a target. The table values are typical starting values for a rigid machine. A lighter hobby machine, a long cutter or a loose hold-down may need a lower chip load and a shallower cut. Start low, make a test cut, and raise the feed in small steps while watching the chips and the finish.