# What is the SFM, rpm and feed rate? Works out the spindle speed in rpm from the surface speed (SFM or m/min) and the tool diameter, or the SFM from the rpm, and the feed rate from the chip load and the number of flutes. - Page: https://www.acalculator.org/physics/speeds-and-feeds-calculator - JSON spec: https://www.acalculator.org/physics/speeds-and-feeds-calculator.json - Version: 716d31704df2 ## Default answer Example with the default inputs (Units Inch, Find RPM, Tool diameter 0.5, Surface speed 300, Chip load 0.002, Flutes 4): Run the spindle at 2,292 rpm for a surface speed of 300. ## Inputs | Key | Label | Description | | --- | --- | --- | | units | Units | Inch units (SFM, inches, in/min) or metric (m/min, millimeters, mm/min). | | find | Find | The spindle speed from the surface speed, or the surface speed from the spindle speed. | | d | Tool diameter | The cutter or drill diameter, in inches (inch units) or millimeters (metric). | | sfm | Surface speed | The cutting speed at the tool’s edge: surface feet per minute (SFM), or meters per minute in metric. | | rpm | Spindle speed (rpm) | The spindle speed in revolutions per minute. | | cl | Chip load | The feed per tooth (per flute): inches per tooth, or millimeters per tooth in metric. | | z | Flutes | The number of cutting teeth (flutes). A drill counts as 1 when the chip load is its feed per revolution. | ## Outputs | Key | Label | Description | | --- | --- | --- | | rpm | Spindle speed (rpm) | N = 12 × SFM ÷ (π × D in inches), or 1,000 × m/min ÷ (π × D in mm). | | speed | Surface speed | SFM = π × D × rpm ÷ 12 (inch), or m/min = π × D × rpm ÷ 1,000 (metric). | | feed | Feed rate | rpm × chip load × flutes: inches per minute, or millimeters per minute in metric. | | perRev | Feed per revolution | Chip load × flutes: inches (or millimeters) per revolution. | | other | Surface speed in the other unit | The surface speed in m/min (inch units) or SFM (metric): 1 ft = 0.3048 m. | ## Method Inch: rpm = 12 × SFM ÷ (π × D), SFM = π × D × rpm ÷ 12. Metric: rpm = 1,000 × Vc ÷ (π × D), Vc = π × D × rpm ÷ 1,000. Feed = rpm × chip load × flutes. ## Assumptions - The surface speed and chip load come from your tool maker or a machining handbook for the tool and material; the calculator does not pick them. - For a drill, type the feed per revolution as the chip load with 1 flute. - Machines often run slower than the formula on manual setups; UF’s example uses 60% of the computed values. ## Worked examples 1. units = inch, find = rpm, d = 0.25, sfm = 100, cl = 0.004, z = 1 gives rpm = 1,527.887454, feed = 6.11155. Source: University of Florida, Mechanical and Aerospace Engineering design lab, Speeds and Feeds (N [rpm] = 12 V [sfm] ÷ (π D [in]); milling feed f [in/min] = N × feed per tooth × number of teeth; a ¼ in drill at 100 sfm runs at about 1,500 rpm and 6 in/min at 0.004 in/rev), https://web.mae.ufl.edu/designlab/Advanced%20Manufacturing/Speeds%20and%20Feeds/Speeds%20and%20Feeds.htm (retrieved 2026-10-02): N = 12 × 100 ÷ (π × 0.25) ≈ 1,500 rpm and f ≈ 6 in/min. 2. units = inch, find = rpm, d = 0.5, sfm = 300, cl = 0.002, z = 4 gives rpm = 2,291.831181, feed = 18.334649, perRev = 0.008, other = 91.44. Source: University of Florida, Mechanical and Aerospace Engineering design lab, Speeds and Feeds (N [rpm] = 12 V [sfm] ÷ (π D [in]); milling feed f [in/min] = N × feed per tooth × number of teeth; a ¼ in drill at 100 sfm runs at about 1,500 rpm and 6 in/min at 0.004 in/rev), https://web.mae.ufl.edu/designlab/Advanced%20Manufacturing/Speeds%20and%20Feeds/Speeds%20and%20Feeds.htm (retrieved 2026-10-02). 3. units = inch, find = sfm, d = 0.5, rpm = 2,000, z = 2 gives sfm = 261.799388. Source: University of Florida, Mechanical and Aerospace Engineering design lab, Speeds and Feeds (N [rpm] = 12 V [sfm] ÷ (π D [in]); milling feed f [in/min] = N × feed per tooth × number of teeth; a ¼ in drill at 100 sfm runs at about 1,500 rpm and 6 in/min at 0.004 in/rev), https://web.mae.ufl.edu/designlab/Advanced%20Manufacturing/Speeds%20and%20Feeds/Speeds%20and%20Feeds.htm (retrieved 2026-10-02). 4. units = metric, find = rpm, d = 10, sfm = 120, cl = 0.05, z = 3 gives rpm = 3,819.718634, feed = 572.957795. Source: Virasak, Manufacturing Processes 4-5, Unit 2: Speed and Feed (Workforce LibreTexts; cutting speed in ft/min or m/min; the shop rule RPM = cutting speed × 4 ÷ diameter, a 3/8 in drill at 100 sfm runs at about 1,066 rpm), https://workforce.libretexts.org/Bookshelves/Manufacturing/Manufacturing_Processes_4-5_(Virasak)/02%3A_Lathe_Machines/02.2%3A_Unit_2%3A_Speed_and_Feed (retrieved 2026-10-02). ## FAQ ### What is SFM? SFM is surface feet per minute: how fast the cutting edge moves past the work. It depends on the tool and work material, not the tool size, so tool makers and handbooks give it per material. The metric version is meters per minute (m/min). ### How do I convert SFM to rpm? rpm = 12 × SFM ÷ (π × D), with D the tool diameter in inches. The 12 turns feet into inches and π × D is the distance the edge travels in one turn. A ½ in end mill at 300 SFM runs at 3,600 ÷ (π × 0.5) ≈ 2,292 rpm. ### What is the "SFM × 4 ÷ D" shop rule? 12 ÷ π is 3.82, which shops round to 4 for quick mental maths: rpm ≈ 4 × SFM ÷ D. A 3/8 in drill at 100 SFM gives 4 × 100 ÷ 0.375 ≈ 1,066 rpm by the rule, against 1,019 rpm by the exact formula. The calculator uses the exact π. ### How do I calculate the feed rate? Feed rate = rpm × chip load × number of flutes. The chip load is how thick a chip each tooth takes. At 2,292 rpm with 4 flutes and a 0.002 in chip load, the feed is 2,292 × 0.002 × 4 ≈ 18.3 in/min. ### How do I use it for drilling? A drill is fed per revolution. Type the feed per revolution as the chip load and set flutes to 1. UF’s example ¼ in drill at 100 SFM runs at about 1,528 rpm, and at 0.004 in per revolution feeds about 6.1 in/min. ### How do I work in metric? Pick metric: the diameter is in millimeters, the surface speed in m/min and the chip load in mm per tooth. Then rpm = 1,000 × Vc ÷ (π × D). A 10 mm cutter at 120 m/min runs at 120,000 ÷ (π × 10) ≈ 3,820 rpm. ## Sources - University of Florida, Mechanical and Aerospace Engineering design lab, Speeds and Feeds (spindle speed and feed rate formulas; worked HSS drill example). https://web.mae.ufl.edu/designlab/Advanced%20Manufacturing/Speeds%20and%20Feeds/Speeds%20and%20Feeds.htm (retrieved 2026-10-02) - Virasak, Manufacturing Processes 4-5, Unit 2: Speed and Feed, Workforce LibreTexts (cutting speed in ft/min or m/min; the RPM = CS × 4 ÷ D shop rule). https://workforce.libretexts.org/Bookshelves/Manufacturing/Manufacturing_Processes_4-5_(Virasak)/02%3A_Lathe_Machines/02.2%3A_Unit_2%3A_Speed_and_Feed (retrieved 2026-10-02)