Router Bit Speed Calculator

Router Bit Speed Calculator for handheld and table routers. Enter the cutting diameter and the material to get the top RPM, the dial number on your router and a starting feed rate.

How the Router Bit Speed Calculator Picks a Safe RPM

The Router Bit Speed Calculator sets a top speed for any router bit from its cutting diameter. It then turns that RPM into a dial number on your router and works out a starting feed rate for the material you are cutting.

It is built for woodworkers running a handheld or table-mounted router with a variable speed dial. It also helps CNC users who want a chip load check on a Freud bit before a test cut.

The top speed comes from the lowest of three limits. The first is Freud's speed chart for the bit's diameter, and the second is any maximum marked on the bit itself. The third is the top speed of your router, and the hero shows which one set the result.

Freud's Speed Limits by Cutting Diameter

Freud's chart caps a bit up to 1 in across at 24,000 RPM and bits from 1 to 1-1/4 in at 18,000. From 1-1/4 to 2-1/4 in the limit is 16,000 RPM, and from 2-1/4 to 3-1/2 in it drops to 12,000. A LumberJocks member posted the same four steps from the card that came with a Freud bit.

The reason bigger bits run slower is rim speed, the speed of the outer cutting edge through the wood. It grows with both diameter and RPM, so doubling the bit's width doubles its edge speed at the same dial setting.

$$V_{rim}=\frac{\pi D\times RPM}{12}$$

With D in inches, the result is in feet per minute. A 1/2 in straight bit at 24,000 RPM moves its edge at 3,142 ft/min, about 36 mph. A 2 in bit at the same RPM would move four times as fast, about 143 mph.

The last column shows something the chart alone hides. Freud's limits hold RPM steady across each size band, so rim speed actually climbs from 71 mph on a 1 in bit to about 125 mph on a 3-1/2 in panel raiser. The chart is a ceiling, not a target, and a speed marked on the bit always comes first.

Measure the Cutting Diameter, Not the Radius

The most common input slip is entering the profile size instead of the bit's width. A 1/2 in radius roundover is not a 1/2 in bit, because its width is the bearing plus the radius on each side.

Freud's 34-116 roundover has a 1/2 in radius but an overall diameter of 1-1/2 in, and Freud marks it for 16,000 RPM maximum. Enter 1.5 in and the calculator returns the same 16,000. Enter 0.5 and it would suggest 24,000, which is 50% faster than the bit's own rating.

Measure across the widest carbide with calipers, not the shank or the bearing. On a bearing-guided bit the carbide wings sweep the widest circle, and many packages print that figure as the overall diameter.

How the Router Bit Speed Calculator Sets Your Dial

Router speed dials show numbers, not RPM, so the first card converts the speed to a dial setting. The Bosch 1617EVS manual lists 8,000, 13,500, 16,500, 20,000, 21,500 and 25,000 RPM for settings 1 to 6. The DeWalt DW618 manual lists 8,000, 12,000, 14,000, 18,000, 21,000 and 24,000.

Both dials turn smoothly between marks, so the calculator gives a decimal setting. The 1-1/2 in roundover at 16,000 RPM lands at about 2.8 on the Bosch and 3.5 on the DeWalt.

DeWalt's own chart adds a useful point. For bits 1/2 in or smaller in hardwood, it rates 21,000 RPM as very good and full speed only as good. For bits over 1-1/8 in, it rates 12,000 very good and anything from 18,000 up as not recommended.

For a router without a chart in the tool, the dial marks are spread evenly across the speed range you enter, and the card labels them as estimates. Your own router's manual chart, if it has one, is always closer than the even spread.

Feed Rate From Freud's Chip Load Chart

Feed rate is how fast the bit moves through the wood. Freud's feed and speed guide sets it from chip load, the thickness of wood each cutting edge takes on every turn.

$$F=RPM\times n\times CL$$

F is feed in inches per minute, n is the number of cutting edges and CL is the chip load in inches. Freud lists separate chip loads for solid carbide spiral bits and carbide-tipped straight and profile bits, across eight materials.

For a 1/2 in two-flute carbide-tipped bit in hardwood, Freud gives 0.008 to 0.010 in. At 24,000 RPM that works out to 384 to 480 in/min. The same size in solid carbide takes 0.018 to 0.021 in, more than twice as much, because the spiral clears chips better.

Freud wrote this chart for CNC routers and says to start at the low end of the range with test cuts in scrap. On a handheld router, the in/sec figure is a ceiling to work up to, not a pace to start at. Freud lists no aluminum chip load for carbide-tipped bits, so the tool asks for solid carbide there.

Chip loads stop at 3/4 in for carbide-tipped bits and 1/2 in for solid carbide. Larger bits use the last row of the chart, since Freud publishes nothing beyond it.

Deeper Passes Need a Lighter Chip

Freud's chip loads assume each pass is no deeper than the bit's diameter. At twice the diameter, Freud says to cut chip load by at least 25%, and at three times by at least 50%.

Freud's own example shows the math. A chip load of 0.019 in on a 1/2 in bit cutting 1 in deep drops to 0.019 times 0.75, about 0.014 in. At 18,000 RPM with two flutes, that trims the feed from 684 to about 504 in/min.

The fourth card shows the depth ratio for your pass, the reduction it calls for and the passes needed to reach full depth. The calculator applies the 25% cut as soon as a pass goes past one diameter and the 50% cut past two, which errs on the lighter side between Freud's steps. Past three times the diameter, the tool warns you to split the cut.

Bit diameter can be 0.03 to 6 in, and cutting edges 1 to 6. Depth per pass runs from 0.005 to 3 in, total depth up to 10 in, and router speeds up to 60,000 RPM. Real results shift with wood density, bit sharpness and router power, so treat every number as a starting point for a test cut.

The same rim speed idea drives the Lathe Speed Calculator, where turners limit diameter times RPM instead. For joinery work on a jig, the Dovetail Calculator sets the tail and pin layout before the router ever starts.

Router Speed Questions From the Shop

What speed should I run a 1/2 inch roundover bit at?

Check the cutting diameter first, since a 1/2 in radius roundover is usually about 1-1/2 in across. Freud's 34-116 is exactly that size and carries a 16,000 RPM maximum, which matches its chart for bits from 1-1/4 to 2-1/4 in.

Smaller roundovers fall into faster bands, but only a bit whose total width stays at or under 1 in can run at 24,000. Check the overall diameter printed on the package, or measure across the carbide.

Should I slow the router down or speed up when it burns?

Woodworkers on the Fine Woodworking forum split on this, and both camps have a point. Burning comes from heat when each edge takes too thin a chip, so either lowering RPM or feeding faster raises the chip load.

By Freud's formula, dropping from 24,000 to 18,000 RPM at the same feed makes each chip a third thicker. The same forum thread adds that stopping mid-cut, especially in corners, burns even a sharp bit, and that cherry and maple scorch more easily.

Can I run a bit rated for 24,000 RPM on a 25,000 RPM router?

Not at full speed. The bit rating is a maximum, and the Bosch 1617EVS tops out at 25,000 RPM on setting 6. A LumberJocks thread on this exact question points out that the dial turns smoothly between marks.

Setting the Bosch dial to about 5.7 puts it at 24,000 RPM. The calculator does this automatically when you enter the bit's rating in the Max RPM Marked on Bit field.

Does a router lose speed when it is cutting?

Older routers did, and one Fine Woodworking member estimates a 20,000 RPM router slows to 15,000 or less under a real cut. Electronic variable-speed routers work differently.

Bosch says its Constant Response circuitry adjusts power to hold the set RPM. DeWalt's DW618 manual says the same, and warns that because the speed does not drop, you can overload the motor without hearing it. It advises a shallower pass or slower feed if the router strains.