Machining unit conversion
Machining Unit Conversion Calculator
Convert common machining units for length, pressure, force, torque, speed, roughness and metric-inch values
Tool Positioning
This tool converts common units used in machining, fixture design, chuck selection and shop-floor communication. It supports metric-inch length conversion, MPa to psi, kN to kgf, N·m to lbf·ft, m/min to SFM, Ra to microinch and reference hardness conversion for HRC, HB and HV. The result is intended for daily engineering reference and quick calculation.
Quick Conversion Modules
Metric-inch size converter
Pressure conversion
Force conversion
Torque conversion
RPM and surface speed conversion
Feed rate conversion
Surface roughness conversion
Ra and Rz cannot be accurately converted using a fixed ratio. This tool only converts Ra between micrometers and microinches.
Area conversion
Volume conversion
Hardness conversion
Hardness conversion is based on interpolation from common steel reference tables, not an exact formula. Material type, heat treatment, test load and surface condition can affect the result.
Hardness conversion results are reference values only. They do not replace hardness tester measurements and must not be used as heat-treatment acceptance or material inspection proof. The current table is for common steel hardness ranges only and does not include HS Shore hardness.
Common machining conversion table
| Category | Common conversion |
|---|---|
| Length | 1 inch = 25.4 mm; 1 mm = 0.03937 inch; 1 µm = 0.001 mm |
| Pressure | 1 MPa = 10 bar; 1 MPa = 145.04 psi; 1 bar = 14.50 psi |
| Force | 1 kN = 101.97 kgf; 1 kgf = 9.80665 N; 1 lbf = 4.44822 N |
| Torque | 1 N·m = 0.73756 lbf·ft; 1 lbf·ft = 1.35582 N·m |
| Roughness | 1 µm Ra = 39.37 µin Ra; 32 µin Ra ≈ 0.81 µm Ra |
Common hardness reference conversion
| HRC | HB | HV | HRB | Reference tensile strength MPa | Note |
|---|---|---|---|---|---|
| 20 | 220 | 220 | 98 | 760 | Steel reference table interpolation only |
| 30 | 285 | 290 | - | 980 | |
| 40 | 375 | 390 | - | 1280 | |
| 50 | 500 | 530 | - | 1650 | |
| 60 | 600 | 745 | - | 2100 |
Formula Notes and Use Boundaries
Length, pressure, force, torque, area and volume use standard unit relationships. RPM and surface speed use V = π × D × n / 1000. Feed rate uses f × n for turning or fz × z × n for milling. Hardness conversion uses reference-table interpolation, not an exact formula.
Suitable Scenarios
Suitable for machining drawing communication, hydraulic pressure reference, clamping-force estimates, bolt torque checks, turning surface speed estimates, feed-rate conversion and roughness unit checks. Formal inspection, heat-treatment acceptance and safety parameters must still follow drawings, standards and inspection reports.
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FAQ
What unit conversions are most common in machining?
Common conversions include mm and inch, MPa and psi, kN and kgf, N·m and lbf·ft, rpm and surface speed, Ra micrometer and Ra microinch, plus area, volume and feed-rate conversions.
How many millimeters are in one inch?
1 inch = 25.4 mm. This is the standard metric-inch relationship used in machining drawings and shop communication. In reverse, 1 mm = 0.0393701 inch.
How do MPa, bar and psi convert?
1 MPa = 10 bar = 145.0377 psi, 1 bar = 0.1 MPa, and 1 psi = 0.00689476 MPa. Hydraulic chuck pressure often uses MPa, while many overseas references use psi.
What is the difference between kN, kgf and lbf?
kN and N are SI force units. kgf is kilogram-force based on standard gravity, and lbf is pound-force. 1 kgf = 9.80665 N and 1 lbf = 4.44822 N.
How do N·m and lbf·ft convert?
1 N·m = 0.737562 lbf·ft, and 1 lbf·ft = 1.35582 N·m. This conversion is common for bolt torque, fixture tightening and spindle torque references.
How are rpm and surface speed converted?
Surface speed V = π × D × n / 1000, where D is in mm, n is rpm, and V is m/min. Imperial surface speed SFM = m/min × 3.28084.
How do Ra micrometer and Ra microinch convert?
For Ra units, 1 µm = 39.3701 µin and 1 µin = 0.0254 µm. This tool only converts Ra units and does not treat Ra and Rz as a fixed-ratio conversion.
Can Ra and Rz be directly converted?
No. Ra and Rz describe different roughness parameters. Machining method, tool marks and measurement conditions change the relationship, so drawings should be inspected by the specified roughness parameter.
Can HRC, HB and HV be converted exactly?
No. HRC, HRB, HB and HV come from different hardness test methods. This tool interpolates common steel reference tables only; formal inspection must use the specified hardness tester and acceptance standard.
Can the conversion results be used for engineering communication?
Yes, they are suitable for daily communication, preliminary calculation and data checks, but they do not replace formal drawings, tolerance standards, inspection reports or heat-treatment acceptance criteria.