Half of Inch Fractions Table
| Fraction | Half | Decimal | mm |
|---|---|---|---|
| 1” | 1/2” | 0.5 | 12.70 |
| 7/8” | 7/16” | 0.4375 | 11.11 |
| 3/4” | 3/8” | 0.375 | 9.53 |
| 5/8” | 5/16” | 0.3125 | 7.94 |
| 1/2” | 1/4” | 0.25 | 6.35 |
| 3/8” | 3/16” | 0.1875 | 4.76 |
| 1/4” | 1/8” | 0.125 | 3.18 |
| 1/8” | 1/16” | 0.0625 | 1.59 |
| 1/16” | 1/32” | 0.03125 | 0.79 |
| 1/32” | 1/64” | 0.015625 | 0.40 |
| Situation | The halving that matters |
|---|---|
| Sawing stock down the middle | 3/4” board → two 3/8” faces - account for the blade kerf before you mark |
| Sewing seam allowances | 5/8” pattern seam → 5/16” trimmed or topstitched; 1/4” → 1/8” at collars |
| Framing and layout | Center = measure whole, take half from the table, mark from one edge - the eye centers high |
| Shelf pin holes | 1/4” system halved is 1/8” - below that you are drilling metric, not fractions |
| Below the table | Half of 1/64” is 1/128” (0.20 mm) - real math, no tape mark; calipers take over |
Halving an inch fraction trips people because the answer is never a number you can point to on the tape's printed scale - half of 3/8 inch is 3/16, and the 3/16 mark is a tick, not a numeral. The rule is one line: to halve a fraction, double the denominator and keep the numerator (half of n/16 is n/32). That is why the halving chain always marches toward 64ths and why the table reads like a countdown: 1, 1/2, 1/4, 1/8, 1/16, 1/32, 1/64.
Bottom line: odd numerators are the actual lookup need - half of 3/4 is 3/8 and half of 5/8 is 5/16 are the two every woodworker and sewist hits first - while even numerators halve by cancellation (half of 6/16 is 3/8, not 6/32). The table carries both forms plus the decimal and millimeter values, because half a millimeter is where cutting accuracy actually lives: 1/16 inch is 1.6 mm, and half of that is already inside the kerf of most saw blades.
The honest part: below 1/64 the tape measure has no marks at all - the fractions keep halving forever mathematically, but physically you have crossed from measuring into calipers and micrometers. And halving is not the same as estimating: for layout work, find the center by measuring the whole and marking half of the measurement, not by eye - the eye centers high, consistently, which is why the last inch of every shelf fits worse than the first.
How to use
- Halve with the rule, not the eye: double the denominator, keep the numerator - half of 5/8 is 5/16, half of 7/16 is 7/32. For even numerators, cancel instead: half of 6/16 is 3/8.
- Read the answer off the table in the unit you are actually cutting in: the decimal column for digital calipers, the millimeter column for plans drawn metric, the fraction column for tape and ruler work.
- Stop halving where the tool stops: 1/64 is the last mark a tape carries; below that, calipers. If the halved size matters (a tenon, a seam allowance), test-fit before cutting the second piece.
Frequently asked questions
What is half of 3/8 inch?
3/16 inch. Double the denominator (8 to 16), keep the numerator: half of 3/8 = 3/16 = 0.1875 inch, about 4.76 mm. It is the most-looked-up halving in woodworking because 3/8 stock splits into two 3/16 faces, and 3/16 is a tick below the 1/4 mark - closer to it than to 1/8.
What is half of 5/8 inch?
5/16 inch (0.3125, about 7.94 mm) - the second-most-looked-up value, since 5/8 is a standard material thickness (deck boards, plywood strips) and its half lands on 5/16, a tick the tape carries but no numeral labels. Same rule: 8 doubles to 16, the 5 rides along.
Why is half of 1/4 not 1/2?
Because 'half' sends the size down, not the numeral up: half of 1/4 inch is 1/8 inch. The denominator doubles (4 to 8) while the part of the inch stays the same share of a smaller whole - it reads backwards against intuition because the printed numerals on a tape (1/4, 1/2) get bigger while the marks they label get closer together.
How do you halve a fraction with an even numerator?
Cancel first, then halve: half of 6/16 is not 6/32 - that is unsimplified. Half of 6/16 = 3/16... wait, do it cleanly: 6/16 reduces to 3/8, and half of 3/8 is 3/16. The fast pattern: halve the numerator when it is even (6/16 to 3/16 works only if you also keep the denominator - 6/16 halved is 3/16, yes, because 6 halves to 3 and 16 stays). Both routes land on 3/16; the doubling-denominator route is the one that never fails.
What is half of 1/16, 1/32, and 1/64 inch?
Half of 1/16 is 1/32 (0.03125, about 0.79 mm); half of 1/32 is 1/64 (about 0.40 mm); half of 1/64 is 1/128 - a real fraction with no tape mark anywhere. Practical floor: 1/64 is the last line most tapes and rules carry, so most shops answer 'half of 1/64' with 'calipers', not with a fraction.
Is halving inches different from halving centimeters?
No - halving is unit-free: half of 3 cm is 1.5 cm the same way half of 3/8 inch is 3/16 inch. What differs is the resolution floor: metric tapes print millimeters all the way down, so 'half of a millimeter' is still a readable mark (0.5 mm), while the imperial side runs out of printed ticks at 1/64. That is the whole reason metric countries layout at odd sizes comfortably and imperial shops keep a fraction-to-decimal card taped to the saw.