Speeds and Feeds Calculator
Enter your cutter diameter, number of flutes, surface speed and chipload to calculate spindle RPM, feed rate, and material removal rate for milling, drilling and routing. Choose a material and tool material to auto-fill recommended starting values, then fine-tune the settings. Switch between imperial and metric units at any time.
What are speeds and feeds in machining?
Speeds and feeds are the two fundamental parameters that control how a cutting tool removes material. "Speed" refers to the spindle RPM or, more precisely, the surface speed (the relative velocity at the cutting edge measured in surface feet per minute, SFM, or metres per minute, m/min). "Feeds" refers to how quickly the workpiece or tool advances, typically expressed as feed rate in inches per minute (IPM) or millimetres per minute (mm/min) for milling, or as feed per tooth (chipload, IPT) for individual cutting edges. Getting both right is critical: too slow wastes time and can cause rubbing rather than cutting; too fast breaks tools, leaves a poor surface and can damage the machine.
How to use the calculator
Select your operation (milling, drilling or turning), tool material (carbide or HSS) and workpiece material. The calculator automatically fills in recommended surface speed and chipload values as starting points. Enter your actual cutter diameter and flute count, then adjust the surface speed and chipload if needed. The spindle RPM and feed rate update instantly. For milling, add axial depth of cut (how deep the cutter goes) and radial width of cut (the stepover) to see the material removal rate (MRR). To convert between units, toggle the Units selector at the top.
The formulas behind the calculations
Spindle RPM is derived from surface speed and tool diameter: RPM = (12 x SFM) / (pi x D_inches). In metric: RPM = (1000 x Vc_m/min) / (pi x D_mm). Feed rate for milling and drilling is: Feed (IPM) = Chipload x Number of Flutes x RPM. Material removal rate ties all three cutting dimensions together: MRR (in3/min) = Feed Rate x Axial DOC x Radial DOC. Higher MRR means faster machining but also more load on the cutter and spindle, so machine rigidity sets the practical upper limit. For turning, the spindle RPM formula is the same but the "diameter" is that of the rotating workpiece, and feed rate is given as inches per revolution (IPR) rather than per minute.
Choosing between carbide and HSS tooling
Carbide (cemented tungsten carbide) is harder, stiffer and more heat-resistant than high-speed steel. It can run at surface speeds 3 to 5 times higher than HSS, which means dramatically faster cycle times when your machine has the rigidity and spindle speed to take advantage of it. HSS is tougher, cheaper and better at absorbing vibration, making it preferable on older or lighter machines, for interrupted cuts, and for operations where tool cost matters more than cycle time. Most modern CNC machining centres use carbide as the default; manual mills and hobby CNCs often use HSS or carbide-tipped tools as a cost-effective middle ground. The reference table on this page lists recommended surface speeds for both tool materials across ten common workpiece materials.
Recommended surface speeds and chiploads by material
| Material | HSS SFM | Carbide SFM | HSS IPT (1/2" EM) | Carbide IPT (1/2" EM) |
|---|---|---|---|---|
| Aluminum / Aluminum Alloys | 200 | 700 | 0.005 | 0.008 |
| Brass / Bronze | 150 | 350 | 0.004 | 0.006 |
| Cast Iron | 60 | 300 | 0.003 | 0.005 |
| Mild Steel (1018, A36) | 90 | 400 | 0.002 | 0.004 |
| Alloy Steel (4140, 4340) | 60 | 250 | 0.002 | 0.003 |
| Stainless Steel (304, 316) | 50 | 200 | 0.001 | 0.002 |
| Titanium (Ti-6Al-4V) | 30 | 120 | 0.001 | 0.002 |
| Hardwood (Oak, Maple) | 400 | 800 | 0.010 | 0.015 |
| Softwood (Pine, MDF) | 500 | 1000 | 0.012 | 0.020 |
| Plastic / Acrylic (HDPE, Nylon) | 300 | 600 | 0.006 | 0.010 |
Starting values for solid carbide and HSS end mills. Adjust based on machine rigidity, cutter condition and coolant availability. Carbide can run 3-5x faster than HSS.
Frequently asked questions
What is the difference between RPM and surface speed (SFM)?
RPM is how many full turns the spindle makes per minute. Surface speed (SFM) is the linear speed of the cutting edge relative to the workpiece, taking the tool diameter into account. A 1-inch cutter at 1000 RPM has a much higher surface speed than a 0.1-inch cutter at the same RPM, because the edge of the larger cutter travels a longer arc per revolution. When you look up recommended speeds in a reference chart, you almost always find SFM because that reflects what the cutting edge actually experiences regardless of tool size. The calculator converts SFM to RPM automatically once you enter the tool diameter.
What is chipload and why does it matter?
Chipload (feed per tooth, IPT) is the thickness of the chip each cutting edge removes in one revolution. It is the single most important parameter for cutter health and surface finish. Too low a chipload causes rubbing rather than cutting: the tool heats up through friction, the edge dulls rapidly, and the surface looks polished but torn. Too high a chipload overloads each tooth and can snap the cutter. The right chipload for a given tool and material produces a well-formed chip that carries heat away from the cutting zone. Recommended values scale with cutter diameter: a larger cutter can take a thicker chip.
How do I find the right surface speed for my material?
Select your workpiece material and tool material in the calculator and it will pre-fill the recommended surface speed. The reference table lower on this page also lists SFM ranges for ten common materials with both HSS and carbide tooling. As a rough rule: aluminium, brass and plastics allow high speeds; mild steel is moderate; stainless steel, alloy steel and titanium require low speeds because they generate more heat. Always treat tabulated values as starting points and adjust based on your actual cut conditions, machine rigidity and coolant availability.
What is material removal rate (MRR) and why should I care?
Material removal rate (MRR) measures how fast you are actually removing material in cubic inches per minute (or cm3/min in metric). It combines feed rate, axial depth of cut and radial width of cut into a single productivity number. A higher MRR means shorter cycle times and lower cost per part, but it also means more load on the tool, spindle and workpiece fixture. MRR is useful for comparing the efficiency of different cutting strategies: for example, a shallow but fast high-speed machining pass versus a slow but deep conventional pass. You can also use MRR to estimate cycle time if you know the total volume to be removed.
Why does the number of flutes affect feed rate?
More flutes means more cutting edges engaging the material per revolution. For a given chipload (feed per tooth) and RPM, doubling the number of flutes doubles the feed rate. This is why 4-flute end mills are common in steel: you can maintain a conservative chipload per tooth while still achieving a useful feed rate. In aluminium, 2- or 3-flute cutters are preferred because their larger flute gullets give chips room to evacuate before the next tooth comes around - a 4-flute cutter in aluminium can pack chips into the flutes and weld them to the cutting edge.