Surface Finish Calculator 2026
Calculate theoretical surface roughness (Ra, Rz, Rmax) for turning, milling, and grinding. Predict finish quality and find suitable applications per ISO 4287.
Surface Finish Calculator
Predict surface roughness based on cutting parameters
Ra Formula
Ra = f² / (32 × r)Ra = Surface roughness (μm)
f = Feed per revolution (mm)
r = Tool nose radius (mm)
💡 ISO N-Classes
Understanding Surface Finish
What is Ra?
Ra (Roughness Average) is the most common surface finish parameter, defined in ISO 4287. It represents the arithmetic average of profile deviations from the mean line, measured in micrometers (μm). Lower Ra values indicate smoother surfaces.
Theoretical vs. Actual Finish
Theoretical Ra is calculated from geometry alone: Ra = f²/(32×r). Actual finish is typically 1.2-2.0× worse due to tool wear, machine vibration, material properties, and built-up edge. This calculator applies correction factors to estimate realistic values.
Improve Finish
- • Reduce feed rate
- • Increase nose radius
- • Use flood coolant
- • Ensure tool sharpness
Finish Killers
- • High feed rate
- • Worn tools
- • Vibration/chatter
- • Built-up edge
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Frequently Asked Questions
Ra (Roughness Average) is the arithmetic average of surface profile deviations from the mean line, measured in micrometers (μm). It is the most common surface roughness parameter per ISO 4287. Ra is measured using profilometers that trace a stylus across the surface. Typical Ra values: Mirror finish 0.025 μm, Fine machining 0.8-1.6 μm, General machining 3.2-6.3 μm.