What is the independence principle (ISO 8015)?

The independence principle states that each geometrical requirement (size, form, orientation, location) is independent unless otherwise specified. Size tolerance does not control form, and form tolerance does not control size.

What is the envelope requirement?

The envelope requirement (Ⓔ) requires that the feature's surface does not violate a perfect-form boundary at MMC (Maximum Material Condition). This creates a dependency between size and form — at MMC, form must be perfect.

When is the envelope requirement applied?

The envelope requirement is applied when Ⓔ is indicated on the drawing after the size tolerance, or when the drawing references ISO 14405 with the Ⓔ modifier. It is typically used for features that must fit/assemble.

How does independence principle affect inspection?

Under independence principle, size and form are checked separately. Size is checked with two-point measurement (micrometer). Form is checked independently (e.g., roundness tester). Under envelope requirement, a functional gauge at MMC size checks both simultaneously.

What is the difference between ISO 8015 and ASME Y14.5?

ISO 8015 defaults to the independence principle (size and form independent). ASME Y14.5 (Rule #1) defaults to the envelope requirement (perfect form at MMC). This is a fundamental difference between ISO and ASME drawing interpretation.

Free Engineering Tool

ISO 8015 Independence Principle Calculator

Check feature compliance with ISO 8015 independence principle and envelope requirement. Enter size tolerance, form tolerance, and measured values.

ISO 8015Envelope ⒺIndependence

Compliance Check

Overall Verdict

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Size Check (2-point)

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Form Check

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Envelope Check (if Ⓔ)

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MMC / LMC Sizes

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Independence Principle (Default ISO)

Per ISO 8015, each requirement specified on a drawing is independent unless otherwise stated. Size tolerance and form tolerance are verified separately.

Envelope Requirement (Ⓔ)

When Ⓔ is applied, the feature must not violate a perfect-form envelope at MMC size. This means:

For shafts: no local diameter exceeds MMC, and the feature fits inside a perfect cylinder of MMC diameter
For holes: no local diameter is less than MMC, and the feature contains a perfect cylinder of MMC diameter

⚠️ ISO vs ASME: ISO defaults to independence (ISO 8015). ASME Y14.5 Rule #1 defaults to envelope requirement. Be careful when working with drawings from different standards.

ISO 8015 Independence Principle Calculator | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Compliance Check

Independence Principle (Default ISO)

Envelope Requirement (Ⓔ)