16 mm to inches

Formula: inches = millimeters ÷ 25.4 (exact). Or multiply by 0.0393701 for a quick estimate of the same definition.

1. Start with 16 mm.
2. Divide by 25.4: 16 ÷ 25.4 = 0.6299 in.
3. Reverse check: 0.6299 × 25.4 = 16 — the conversion round-trips cleanly.

Dividing by 25.4 is exact: 16 ÷ 25.4 = 0.629921 in, shown as 0.6299 in. The 5/8 in reading is the nearest 1/64, 0.125 mm smaller than 16 mm, not a second exact size.

The decimal column is exact (shown to four places). The fraction is the nearest 1/64 approximation used on rulers and bit charts — so the two can disagree. Here, 16 mm = 0.6299 in exactly, while 5/8 in differs by -0.125 mm. The converter disclaimer (“rounded to the nearest 1/64 fraction”) exists so that difference is never mistaken for a data error.

No. 5/8 in equals 15.875 mm, so 16 mm is 0.125 mm larger. The exact decimal is 0.6299 in, and 5/8 in is the nearest 1/64 tick (0.625 in). A 16 mm drill bit, a 16 mm socket, or a 16 mm wood dowel should stay metric when the fit is tight; 5/8 in is the closest imperial stand-in, not an equal.

Compared with 5/8 in (15.88 mm): 16 mm is +0.125 mm (metric size is larger).

This page is for specification checks — drill bits, sockets, tubing, and stock — not body measurements. For shop picks across many metric diameters, see the drill bit & socket mm to inches chart.

A 16 mm socket is 0.6299 in across the flats. 5/8 in is 15.875 mm — 0.125 mm undersize — so it may turn a fresh 16 mm hex and still cam out once the corners wear. Many automotive spark plugs use a 16 mm hex (often dual-marked 5/8 in); use the 16 mm socket when the plug is metric. A 16 mm drill bit cuts 0.6299 in. A 5/8 in bit cuts 15.875 mm and leaves a hole 0.125 mm smaller, tight for a 16 mm dowel or shank.