Surface Finish Ra to Rz Calculator

Convert surface roughness Ra (µm) to Rz (µm) instantly. This tool is widely used in CNC machining, precision engineering, and surface finish specification to quickly estimate roughness equivalence.

Ra To Rz
Calculator

Ra
Rz
Ra 0 µm ≈ Rz 0 µm
Approximate conversion: Rz ≈ Ra × 7
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Note: Ra to Rz conversion is approximate. A commonly used estimation is Rz ≈ Ra × 7, but the actual relationship depends on machining process, material, surface profile, and measurement standard.

Quick Answer

  • Rz ≈ Ra × 7 (common engineering approximation)
  • Ra ≈ Rz ÷ 7

👉 Fast reference:

  • Ra 1.6 µm ≈ Rz 11.2 µm
  • Ra 3.2 µm ≈ Rz 22.4 µm
  • Ra 0.8 µm ≈ Rz 5.6 µm

⚠️ Note: This is an approximate conversion, actual values depend on machining process and standards.

Formula (Ra to Rz)

Rz ≈ Ra × 7

Ra ≈ Rz ÷ 7

✔ Example:
Ra = 2 µm → Rz ≈ 14 µm

Ra to Rz Conversion Table

Ra (µm) Rz (µm, approx.)
0.2 1.4
0.4 2.8
0.8 5.6
1.6 11.2
3.2 22.4
6.3 44.1
12.5 87.5
25 175

How to Use This Calculator

  1. Enter a value in Ra (µm)
  2. Instantly get the approximate Rz (µm) value
  3. Adjust the value for real-time conversion

✔ Quick estimation for engineering use
✔ No manual calculation needed

Common Engineering Uses

1. CNC Machining Surface Finish

  • Drawings often specify Ra, while inspection may use Rz

2. Supplier Communication

  • Different countries and standards use different roughness parameters

3. Process Capability Matching

  • Turning, milling, grinding produce different Ra–Rz relationships

4. Quality Inspection & Standards

  • ISO (Ra) vs DIN/JIS (Rz) comparisons

Important Notes (Engineering Accuracy)

  • The factor 7 is an approximation, typical range is:
    👉 Rz ≈ Ra × (4 to 10)
  • Depends on:
    • Machining process (turning, grinding, polishing)
    • Material type
    • Measurement method

👉 For critical applications, always refer to actual measurement data or standards.

Related Calculators

Enhance your engineering workflow:

  • Ra to µin Converter
  • Surface Finish Comparison Chart
  • Tolerance Converter (mm ↔ inch)
  • Material Removal Rate Calculator

FAQ

What is Ra?

Ra is the arithmetic average roughness, the most commonly used surface finish parameter.

What is Rz?

Rz is the average peak-to-valley height, representing surface texture more visibly.

Why convert Ra to Rz?

Because different standards and industries use different roughness parameters.

Is Ra × 7 always accurate?

No. It’s an engineering approximation, not a strict conversion.

When should I use Ra vs Rz?

  • Use Ra for general specifications
  • Use Rz when peak/valley height is critical (e.g., sealing surfaces)
CNC Machining Shops

CNC Machining Shops

Need Precision Surface Finish CNC Parts?

Surface finish directly impacts performance, wear, and sealing.

👉 We offer:

  • CNC machining with controlled surface roughness
  • Finishing processes: grinding, polishing, anodizing
  • Ra as low as 0.4 µm or better
  • Full inspection reports available

Upload your drawing today and get a precision quote.