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SAE to metric calculator

Convert a nominal inch dimension to millimetres, or a millimetre dimension to decimal inches.

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Answer

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Convert a nominal inch dimension to millimetres, or a millimetre dimension to decimal inches.

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Precision and calculation record
Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.
Saved scenario
Save the current answer, then change an input to compare. This clears when you leave.
Formula and assumptions
Accepts fractions such as 5/8 and mixed inches such as 1 1/4 in inch mode. Uses exactly 25.4 millimetres per inch. The converted dimension does not establish wrench, socket, thread or fastener interchangeability; no nearest substitute is recommended.
Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.
Scratch calculator
Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.
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Updated 
Using SAE to metric calculator
Convert a nominal inch dimension to millimetres, or a millimetre dimension to decimal inches.
Accepts fractions such as 5/8 and mixed inches such as 1 1/4 in inch mode. Uses exactly 25.4 millimetres per inch. The converted dimension does not establish wrench, socket, thread or fastener interchangeability; no nearest substitute is recommended.
Next: Inch fraction calculator
Next: Length converter
A worked example
For sae inch size (decimal or fraction) = 5/8, direction = Inches to millimetres, dimension (millimetres) = 15.875.
Before you use the result
Accepts fractions such as 5/8 and mixed inches such as 1 1/4 in inch mode. Uses exactly 25.4 millimetres per inch. The converted dimension does not establish wrench, socket, thread or fastener interchangeability; no nearest substitute is recommended.
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ToolOctopus. “SAE to metric calculator.” Updated 2026-09-29. https://tooloctopus.com/sae-to-metric-calculator.
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