Metric CNC programming becomes easier when every quantity is kept in a consistent unit system. The practical problem is that tooling data may arrive in metres per minute, millimetres, mm/rev, mm/tooth, or sometimes in imperial units. This page is focused on keeping those conversions explicit so the final RPM and feed values can be audited.
The basic metric calculator uses cutting speed in m/min, tool or workpiece diameter in mm, flute count and chip load in mm/tooth. The advanced tool adds axial and radial engagement in mm, machine RPM and optional distance in mm. A second use case is checking a metric value that was produced elsewhere and verifying that the unit conversion was not silently changed.
Basic calculation first. Advanced check second.
Run the simple relationship first, then use the advanced version when the operation needs more variables or machine constraints. The calculators are intentionally stacked, not side by side.
Basic Metric machining Speed & Feed Calculator
Run the core calculation for this machining workflow.
Feed Speed Basic
Enter the values you know. The result is calculated in your browser.
Calculation only. Verify toolmaker data, material grade, engagement, machine limits, workholding and actual cutting conditions before production.
Advanced Metric machining Speed & Feed Calculator
Add the relevant process or machine variables for a fuller calculation.
Feed Speed
Enter the values you know. The result is calculated in your browser.
Calculation only. Verify toolmaker data, material grade, engagement, machine limits, workholding and actual cutting conditions before production.
What this speed and feed calculator metric calculates
Keep diameter in millimetres, cutting speed in metres per minute, feed in millimetres per minute, and feed per revolution in millimetres per revolution. For milling, chip load is mm/tooth; for turning and drilling, feed per revolution is normally the more useful unit. Do not assume that every manufacturer chart uses the same convention, and read the table headings before entering values.
Formulas and unit handling
Metric spindle speed uses RPM = (1000 × Vc) ÷ (π × D). Metric milling feed uses Feed = RPM × z × fz. Turning and drilling often use Feed = RPM × f, with f in mm/rev. Useful conversions include 1 inch = 25.4 mm and 1 m/min ≈ 3.28084 ft/min, but conversion should be performed before applying the target formula.
Metric RPM = (1000 × cutting speed in m/min) ÷ (π × diameter in mm).Use the source unit shown in your tooling reference before converting.Milling feed = RPM × flute count × chip load in mm/tooth.Use the source unit shown in your tooling reference before converting.Turning/drilling feed = RPM × feed per revolution in mm/rev.Use the source unit shown in your tooling reference before converting.1 inch = 25.4 mm; 1 m/min ≈ 3.28084 ft/min.Use the source unit shown in your tooling reference before converting.Step-by-step workflow
Technical context for this search
Metric machining becomes reliable when the unit system is explicit from the first field. Cutting speed is commonly stated in m/min, diameter in mm, feed in mm/min, feed per revolution in mm/rev and milling chip load in mm/tooth. The calculator should never rely on a user remembering a hidden conversion. A visible unit label next to every input is part of the engineering workflow, not just a cosmetic feature.
The most common metric mistakes are unit-category mistakes rather than difficult mathematics. SFM is not the same numeric quantity as m/min, and mm/tooth is not interchangeable with mm/rev. A value that looks plausible can still be off by a large factor when the source unit was misunderstood. Always read the heading of the manufacturer chart and keep the original units in the job record before converting anything.
For mixed-unit shops, keep source and programmed values separate. It is acceptable to use an imperial tooling reference and convert the final values, but the conversion should be visible and reversible. This makes audits easier when a programmer, machinist or tooling supplier reviews the setup later. Round only at the final machine-ready stage unless the control or tooling source requires a specific precision.
The metric page also works as a conversion checkpoint for existing programs. Enter the same tool diameter and cutting speed, calculate the RPM, then confirm that the resulting feed matches the source condition after unit conversion. When the result differs, check the variable definition first. Most apparent calculation problems are actually a mismatch between the way two references express speed or feed.
Calculation audit checklist
| Check | What to verify |
|---|---|
| Operation check | Confirm that the job is actually metric machining before entering values. The calculator pair on this page was selected for the speed and feed calculator metric search intent, so switching to another operation may require a different feed convention. |
| Source check | Use the exact tooling or process reference behind speed and feed calculator metric. Record the tool or process identifier, material and source units before converting anything; the site calculates from supplied values rather than selecting proprietary cutting data. |
| Input check | Verify the primary inputs used by the feed-speed-basic and feed-speed calculators. A field can be numerically valid while still being the wrong variable for the operation, especially when moving between chip load, feed/rev, feed rate and surface speed. |
| Unit check | Keep metric and imperial values separated through the calculation. Recheck diameter, cutting speed and feed units on the Speed and Feed Calculator Metric page before accepting the result, and only round after the relationship has been verified. |
| Machine check | Compare the theoretical output with machine spindle, feed, travel and process limits. A calculated value is not a machine capability statement, and a controller limit can make the effective cutting condition different from the selected target. |
| Tool/setup check | Review tool condition, runout, overhang, workholding and coolant or lubrication where relevant to metric machining. These variables are outside the arithmetic model but can dominate the actual cutting result. |
| First-cut check | Treat the first part or first hole as a validation event. Record chips, sound, load, finish and dimensional result alongside the calculated RPM/feed so later changes can be traced to evidence rather than memory. |
| Recordkeeping check | For repeat work, save the source reference, selected inputs, calculated values and final programmed values together. The Speed and Feed Calculator Metric calculation then becomes a reproducible setup record instead of a one-time online number. |
Worked example
A 12 mm cutter at 180 m/min gives approximately 4,775 RPM. With four flutes and a 0.04 mm/tooth chip load, feed is about 764 mm/min. The important point is not the specific example number; it is that the feed was calculated from a consistent metric chain rather than mixing m/min, inches and imperial chip load.
Practical setup checks
Metric mistakes usually happen at the unit boundary. A diameter entered as 0.5 when the calculator expects millimetres can create a result that is mathematically correct but operationally absurd. Watch for tables that switch from mm to inches across columns, and for cutting speed tables that use m/min while chip load tables use in/tooth. Keep a source note beside the number you enter.
Common mistakes
- Entering inch diameter in a metric calculator.
- Treating m/min as if it were SFM.
- Confusing mm/tooth with mm/rev.
- Copying an imperial value into a metric field because the numeric value looks plausible.
- Rounding conversions before the calculation instead of after it.
Troubleshooting the calculated condition
When a metric result looks unrealistic, audit the units before changing the machining inputs. Check whether diameter was supplied in inches, whether surface speed was supplied in SFM, and whether feed was specified per tooth or per revolution. If the source is ambiguous, do not guess; return to the toolmaker’s original document and identify the unit label.
How to cross-check tool data
The best metric workflow keeps the manufacturer’s source unit visible. Convert only after identifying the source column and operation. This page is deliberately explicit about conversions because a conversion error propagates through RPM and feed and can produce a large but internally consistent wrong answer.
Frequently asked questions
What is the metric RPM formula?
RPM = (1000 × cutting speed in m/min) ÷ (π × diameter in mm).
Is chip load the same as feed per revolution?
No. Chip load is normally per cutting edge or tooth in milling, while feed per revolution describes total tool travel for one spindle revolution.
Why is the 1000 factor in the metric RPM formula?
It converts the diameter from millimetres to metres while keeping cutting speed in metres per minute.
Can I use mixed units?
Not safely. Convert the inputs into a single unit system before applying the formula.
This page calculates relationships from the values supplied by the user. It does not inspect the machine, tool condition, workholding or material state. Verify production cutting values against the exact tooling reference and the actual setup before running the cut.