Metric to SAE Calculator

How to use the metric to SAE calculator

What this calculator does. This tool converts one non-negative length among millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. It also compares the exact inch value with common fractional-inch wrench sizes in 1/16-inch steps. That comparison is useful in a workshop, but it does not determine whether substituting one tool for another is mechanically safe.

When to use it. Use it when checking a metric fastener against an SAE wrench set, translating dimensions on drawings, comparing imported and domestic hardware, or converting a field measurement into the units used by a specification. The underlying inch definition is exact: the international inch equals 25.4 millimeters, as documented in the NIST guidance on units of length.

How to calculate. The calculator opens with a demonstration value of 19 millimeters, so every conversion and the example workbook are immediately available.

1. Choose whichever input matches your measurement and replace its demonstration value. You do not need to clear the other fields; they synchronize automatically.
2. Read the exact converted values in the input grid and result cards. The large result identifies the nearest common 1/16-inch SAE size.
3. Review the nearby-size table to see the closest smaller and larger fractional sizes and their differences.
4. Select Download Excel to export the current inputs, outputs, and comparison table as a validated .xlsx workbook.
5. Select Reset to clear all measurement fields and results. Export becomes unavailable until you enter another complete valid value.

Input guide. Length in millimeters, Length in centimeters, Length in meters, and Length in kilometers accept plain decimal metric values. Length in inches, Length in feet, Length in yards, and Length in miles accept plain decimal U.S. customary values. Each field is optional individually, but one field must contain a finite value of zero or greater. Examples include 19 mm, 1.9 cm, 0.019 m, 0.748 in, or 0.0623 ft. Commas, unit letters, fractions such as “3/4,” scientific notation, negative values, and mixed text are rejected rather than silently reinterpreted. Editing any field makes that field the source and recalculates all seven others.

Output guide. Nearest common SAE wrench size rounds the exact inch value to the closest 1/16 inch. Exact inches and Exact millimeters are direct unit identities driven by the active input. Fraction size in millimeters converts the selected fraction back to metric. Absolute fit difference shows the unsigned gap between the measurement and that fraction. The summary pills repeat the active source, exact inches, and nearest fraction. In the table, SAE size is the fraction label, Decimal inches is its exact decimal value, Millimeters uses 25.4 mm per inch, and Difference from input is signed: negative means smaller and positive means larger.

Worked example. With the startup value of 19 mm, divide by 25.4 to obtain 0.748031496 inches. Rounding to the nearest sixteenth gives 12/16, simplified to 3/4 inch. Three-quarters of an inch equals 19.05 mm, so the candidate wrench is 0.05 mm, or about 0.00197 inch, larger than the measured value. The first-open cards, table, and workbook use those same values.

Learn more. NIST's SI measurement overview explains the modern metric framework, while the SI units information center provides practical conversion resources.