What is GPS in dimensional metrology?

GPS (Geometrical Product Specifications) is a framework of ISO standards for specifying and verifying geometry of workpieces. ISO 14405-1 specifically covers linear size tolerances and defines how size is specified and interpreted.

What is the default size specification in ISO 14405-1?

The default specification operator is the two-point size (LP — local size measured between two opposing points). If no modifier is indicated on the drawing, two-point size applies. This is the traditional caliper/micrometer measurement.

What are the special specification operators?

ISO 14405-1 defines several special operators: GG (least-squares/Gaussian size), GX (maximum inscribed size for holes), GN (minimum circumscribed size for shafts), CC (circumference diameter), and others for specific measurement needs.

How does ISO 14405-1 relate to ISO 286?

ISO 286 defines the ISO system of limits and fits (IT grades, fundamental deviations). ISO 14405-1 defines HOW the size is measured/interpreted. Together they fully specify size: ISO 286 gives the limits, ISO 14405-1 gives the measurement method.

What is the envelope requirement (Ⓔ)?

The envelope requirement (Ⓔ modifier per ISO 14405-1) requires that the feature does not violate a perfect-form boundary at MMC. This links size and form, effectively requiring the feature to fit inside a perfect gauge at maximum material size.

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GPS Tolerance Calculator — ISO 14405-1

ISO 14405-1 GPS size tolerance reference. Enter nominal size and fit to see specification operators, limits, and interpretation per the GPS framework.

ISO 14405-1ISO 286GPS Framework

Nominal Size (mm)

Fit / Tolerance

Size Specification Operator

Envelope Requirement

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Drawing Specification

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Upper Limit

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Lower Limit

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Tolerance Band

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Operator Description

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ISO 14405-1 Specification Operators

Symbol	Name	Description	Typical Use
LP	Two-point size	Distance between two opposing points (default)	Caliper/micrometer measurement
GG	Least-squares size	Gaussian (best-fit) diameter	CMM, roundness tester
GX	Max. inscribed size	Largest perfect cylinder that fits inside	Holes (functional gauge)
GN	Min. circumscribed size	Smallest perfect cylinder that fits around	Shafts (functional gauge)
CC	Circumference diameter	Diameter from circumference measurement	Tape measure
CA	Area diameter	Diameter from cross-sectional area	Optical measurement

Default rule: If no specification operator is indicated, LP (two-point size) applies per ISO 14405-1. This is the traditional caliper/micrometer measurement.

GPS Tolerance Calculator | ISO 14405-1 | Free Online Tool

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

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ISO 14405-1 Specification Operators