How this instrument works
Material removal rate, usually shortened to MRR, is a measure of how fast a machining operation clears away stock — not how fast the tool moves or spins, but how much actual volume of material disappears from the workpiece per minute. It's the figure that connects cutting parameters to real production time: two setups can run the same feed rate yet clear very different amounts of metal depending on how wide and deep each pass cuts.
The formula is a straightforward volume-per-time calculation: multiply the width of the cut by its depth to get the cross-sectional area being removed, then multiply that area by the feed rate — how fast the cutter advances through the material — to get a volume cleared per minute. Doubling any one of the three inputs doubles the removal rate; doubling two of them quadruples it, since MRR scales with the product of all three.
Machinists watch this number because it sits at the center of a real tradeoff: pushing MRR higher (via a deeper cut, a wider cut or a faster feed) clears stock faster and cuts cycle time, but also raises cutting forces, heat and tool wear, and can push a setup past what the machine, tool or workpiece can handle without deflection, chatter or premature tool failure. Comparing MRR across different cutting-parameter combinations is how a shop finds the fastest setup a given tool and machine can actually sustain.
- Enter the cut's side-to-side extent into Width of cut (in) — how wide a swath the tool is removing.
- Enter the cut's depth into Depth of cut (in) — how far the tool is plunged into the material.
- Enter the tool's travel speed into Feed rate (in/min) — how fast the cutter advances through the workpiece.
- Read Material removal rate (in³/min) for the volume of stock cleared every minute at those settings.
- Compare MRR across a few width/depth/feed combinations before committing to a setup — a shallow, fast pass and a deep, slow one can share the same removal rate yet load the tool very differently.
Worked example — a 0.5-inch by 0.1-inch cut at 20 in/min
Enter 0.5 into Width of cut (in), 0.1 into Depth of cut (in) and 20 into Feed rate (in/min). Material removal rate (in³/min) reads 1.0000 in³/min.
By hand: the cross-sectional area of the cut is 0.5 × 0.1 = 0.05 in², and multiplying that by the 20 in/min feed rate gives 0.05 × 20 = 1.0 in³/min exactly — one cubic inch of stock cleared every minute at these settings, a clean round number useful for sanity-checking the formula on paper.
Questions
Does MRR account for the specific material being cut?
No — this formula only computes volume removed per minute from geometry and feed rate; it doesn't factor in how hard the material is to cut. A higher MRR is achievable on aluminum than on hardened tool steel with the same tool and machine, but that limit comes from the material's properties and the tool's capability, not from this formula itself, which just reports the volumetric rate for whatever numbers you enter.
Why does doubling the feed rate double the MRR, but doubling width and depth together quadruples it?
Because MRR is the product of three independent quantities. Changing one input scales the result by that same factor — double the feed rate alone, and MRR doubles. But changing two inputs at once compounds: doubling both width and depth doubles the cross-sectional area twice over, so the removal rate rises by a factor of four, even though the feed rate never changed.
Is a higher material removal rate always better?
Not necessarily — a higher MRR clears stock faster and cuts cycle time, but it also raises cutting forces, heat generation and tool wear, and can push a setup past what the machine rigidity, tool strength or workpiece can handle without deflection or chatter. Shops typically look for the highest MRR a given tool and machine combination can sustain reliably, not the highest number achievable on paper.
Does this MRR formula apply to both milling and turning?
The width-times-depth-times-feed-rate structure is a general volumetric removal-rate calculation that applies to any operation where those three quantities are well defined, including slab milling and straight turning passes. Some operations (like plunge milling or complex contour cuts) define width, depth and feed differently, so check that your specific operation's cut geometry matches this formula's assumptions before relying on the number.
What units does this instrument use for the result?
Cubic inches per minute (in³/min), based on width and depth entered in inches and feed rate entered in inches per minute. If your shop works in metric units, convert width, depth and feed rate to consistent metric units first (millimetres and mm/min, for example), then apply the same width × depth × feed formula to get cubic millimetres per minute.