15/16 Wrench to mm | Exact Conversion & Closest Metric Size

A 15/16‑inch wrench measures exactly 23.8125 mm; the closest common metric wrench size is 24 mm.

For the full breakdown, see our best 15/16 Wrench guide.

If you’re working with a 15/16‑inch fastener and only have metric wrenches handy, the direct conversion is 23.8125 millimeters. Because most metric wrench sets skip fractional sizes, hardware stores and mechanics treat 24 mm as the practical replacement for 15/16 inch. This guide explains the math, the common rounding, and what to watch for when swapping sizes.

15/16 to mm: Exact Conversion and Practical Metric Match

The exact equivalent of 15/16 inch in millimeters is 23.8125 mm, calculated by the standard conversion 1 inch = 25.4 mm. To find this: convert 15/16 to a decimal (0.9375) and multiply by 25.4. The result is 23.8125.

Most tool conversion charts, including Misumi’s wrench conversion chart, list 15/16 inch and 24 mm as companion sizes. The difference—just 0.1875 mm—is small enough that a 24 mm wrench will fit a 15/16 fastener in most routine jobs, though the fit may feel slightly tight or loose depending on tolerances. For a quick reference, here are common SAE‑to‑metric pairs:

For official reference, the University of Missouri Extension publishes a standard‑metric wrench chart that pairs 15/16″ with 24 mm as a practical match.

How to Convert SAE to Metric Wrench Sizes

Converting any fractional inch size to millimeters is straightforward:

• Write the fraction as a decimal (divide numerator by denominator).
• Multiply the decimal by 25.4.
• The result is the exact millimeter measurement.
• Compare that to standard metric wrench sizes (e.g., 10 mm, 11 mm, 12 mm…) to find the closest match.

Remember: wrench and socket sizes are measured across the flats of the fastener head, not by the bolt’s diameter. A 15/16 wrench fits the flats, not the shank.

Important Fit and Compatibility Notes

While 24 mm is the standard companion for 15/16 inch, the two are not identical. The 0.1875 mm gap can matter on high‑torque applications, corroded fasteners, or soft metals. Using a near‑size wrench increases the risk of rounding the bolt head. If the fastener is rusted, rounded, or made of soft material like aluminum, always use the exact SAE size or a six‑point socket for better grip. Many mechanics carry mixed SAE/metric sets precisely because real‑world fasteners span both standards, and quality 15/16 wrenches are built to avoid slip‑induced damage.

For everyday home repairs and automotive work, a 24 mm wrench will do the job on a 15/16 fastener. Always test‑fit before applying full torque to ensure a snug, secure grip.