Surface Roughness Converter (Ra ⇄ Rz, RMS, N grade)
Convert Ra to estimated Rz, RMS (Rq), micro-inch CLA and the ISO N grade — the cross-reference every drawing review needs.
Ra and Rz measure genuinely different things — an average versus a peak-to-valley height — so no exact conversion exists. The ×4 rule is the accepted estimate for ground and milled surfaces; turned and EDM textures run anywhere from ×4 to ×7. When a German drawing says Rz 25 and your tester reads Ra, quote Ra ≈ 6.3 µm but flag it as an estimate, and measure Rz directly if the surface seals or slides.
Formula
Note: Estimation ratios only. If the print's roughness callout is functional (sealing faces, bearings, fatigue-critical), measure the specified parameter — never convert and certify.
Convert Ra to estimated Rz, RMS (Rq), micro-inch CLA and the ISO N grade — the cross-reference every drawing review needs. A free machinist & fabrication essentials tool — no sign-up, no upload, instant results in your browser.
About Surface Roughness Converter (Ra ⇄ Rz, RMS, N grade)
Surface Roughness Converter (Ra ⇄ Rz, RMS, N grade) computes the governing relationship Rz ≈ 4·Ra (ground/milled) ; Rq ≈ 1.11·Ra ; N grade: Ra = 0.025·2^(N−1) µm live as you type. Ra and Rz measure genuinely different things — an average versus a peak-to-valley height — so no exact conversion exists. The ×4 rule is the accepted estimate for ground and milled surfaces; turned and EDM textures run anywhere from ×4 to ×7. When a German drawing says Rz 25 and your tester reads Ra, quote Ra ≈ 6.3 µm but flag it as an estimate, and measure Rz directly if the surface seals or slides. Defaults are pre-filled with realistic values for this exact scenario, and the worked example substitutes your numbers step by step so the math is never a black box.
How to use Surface Roughness Converter (Ra ⇄ Rz, RMS, N grade)
- 1Enter your values — Ra (arithmetic mean) (sensible defaults are pre-filled).
- 2Read the live results: Rz (est., ×4 rule), Rq / RMS (≈1.11×Ra), Ra in micro-inch (CLA), ISO roughness grade N.
- 3Check the "with your numbers" line to see Rz ≈ 4·Ra (ground/milled) ; Rq ≈ 1.11·Ra ; N grade: Ra = 0.025·2^(N−1) µm substituted step by step.
- 4Adjust inputs until the scenario matches yours, then copy or share the result.
Why use Surface Roughness Converter (Ra ⇄ Rz, RMS, N grade)?
- ✓Instant, free and private — every calculation runs client-side in your browser; nothing is uploaded
- ✓Built on the stated formula Rz ≈ 4·Ra (ground/milled) ; Rq ≈ 1.11·Ra ; N grade: Ra = 0.025·2^(N−1) µm with authoritative sources cited on the page (ASME B46.1 / ISO 21920 — Surface texture parameters; Machinery's Handbook, 31st ed.)
- ✓Ra and Rz measure genuinely different things — an average versus a peak-to-valley height — so no exact conversion exists.
- ✓Niche-specific defaults give a meaningful worked answer the moment the page loads
Frequently asked questions
What formula does the surface roughness converter (ra ⇄ rz, rms, n grade) use?+
It evaluates Rz ≈ 4·Ra (ground/milled) ; Rq ≈ 1.11·Ra ; N grade: Ra = 0.025·2^(N−1) µm, exactly as published. Sources: ASME B46.1 / ISO 21920 — Surface texture parameters; Machinery's Handbook, 31st ed.. The substituted worked example on the page lets you verify every step against the textbook.
How should I read the result — and how far can I trust it?+
Ra and Rz measure genuinely different things — an average versus a peak-to-valley height — so no exact conversion exists. Estimation ratios only. If the print's roughness callout is functional (sealing faces, bearings, fatigue-critical), measure the specified parameter — never convert and certify.
When is this calculator the right tool for the job?+
Convert Ra to estimated Rz, RMS (Rq), micro-inch CLA and the ISO N grade. The ×4 rule is the accepted estimate for ground and milled surfaces; turned and EDM textures run anywhere from ×4 to ×7. For neighbouring scenarios, the related tools below cover the same engine with different presets.
Do I need to install anything or create an account?+
No. The tool is pure client-side JavaScript: open the page and it works, offline once loaded, with no account, no quota and no data leaving your device.
Related tools
- Shrink Fit Temperature Calculator
- O-Ring Groove Calculator (Gland Design)
- Sine Bar Calculator (Gauge Block Stack)
- V-Belt Length Calculator
- Roller Chain Length Calculator
- Keyway Dimensions Calculator (DIN 6885)
- Countersink Depth Calculator
- Tap Drill & Tapping Speed — M6×1.0 in Steel
- Servo & Reducer Sizing — Wrist (Axis 5)
Related Manufacturing tools
Spindle Speed Calculator — Aluminum 6061
Carbide starting RPM for milling Aluminum 6061: n = 1000·Vc/(π·D) with a handbook cutting speed preset.
● LiveSpindle Speed Calculator — Mild Steel 1018
Carbide starting RPM for milling Mild Steel 1018: n = 1000·Vc/(π·D) with a handbook cutting speed preset.
● LiveSpindle Speed Calculator — Stainless 304
Carbide starting RPM for milling Stainless 304: n = 1000·Vc/(π·D) with a handbook cutting speed preset.
● Live