Read a Fraction Off the Tape and Get a Decimal Inch
A tape measure speaks in sixteenths. A caliper, a CAD dimension box and a CNC post-processor all speak in thousandths. This page sits between the two: type the fraction you just read off the rule and the decimal inch appears in the field underneath while you are still holding the tape.
It is the same arithmetic a machinist does in their head — top number divided by bottom number — but done on every keystroke, which matters when you are working through a cut list of twenty dimensions and do not want a mental slip halfway down the column.
Cut Lists and Setup Sheets
Drill and Tap Charts
CAD and CNC Entry Boxes
Turning a Shop Measurement Into a Decimal
Key the fraction into the top field
Type the numerator, the slash, then the denominator — 7/16, 3/32, 27/64. The field only accepts digits and the slash key, so a stray letter or a decimal point simply will not go in and cannot corrupt the reading.
Read the decimal inch below
The lower field fills in as you type — no button, no page reload. For a measurement over an inch, enter it top-heavy: 1⅜ in goes in as 11/8 and comes back as 1.375.
Copy it into your drawing or offset table
The copy icon inside the decimal field puts the bare number on the clipboard — no unit, no stray spaces — ready to paste into a dimension box, an offsets page or a spreadsheet column.
Going the other way
The arrow button between the fields opens the reverse page — decimal in, fraction out — and carries whatever is currently in the lower field across with it, so a caliper reading of 0.3125 lands there ready to be turned back into 5/16.
3/2 instead — same value, same 1.5 result.Tape-Measure and Drill-Chart Fractions in Decimal Inches
Framing and general carpentry live at 1/16 in. Finish work and joinery drop to 1/32 in. Toolroom and fixture work go to 1/64 in, which is where the fractions stop being memorable and a converter starts earning its keep. Every value below is what this page returns.
| Fraction on the rule | Decimal inch | Where it turns up |
|---|---|---|
| 1/64 | 0.015625 | Toolroom shim and fixture work |
| 1/32 | 0.03125 | Finish carpentry and joinery fits |
| 3/64 | 0.046875 | Small pilot holes |
| 1/16 | 0.0625 | The standard tape-measure division |
| 3/32 | 0.09375 | Thin sheet and veneer thicknesses |
| 1/8 | 0.125 | Common hardboard and acrylic stock |
| 13/64 | 0.203125 | Fractional stand-in for the 1/4-20 tap drill |
| 1/4 | 0.25 | Router bit shank and plywood grades |
| 5/16 | 0.3125 | Tap drill for 3/8-16 threads |
| 3/8 | 0.375 | Dowel and mortise widths |
| 27/64 | 0.421875 | Tap drill for 1/2-13 threads |
| 7/16 | 0.4375 | Across the flats of a 1/4-20 hex head |
| 1/2 | 0.5 | Half-inch stock, bits and collets |
| 5/8 | 0.625 | Drywall sheet and bearing bores |
| 3/4 | 0.75 | Nominal hardwood and ply thickness |
Notice the pattern in the right-hand column of decimals: every halving of the denominator halves the decimal too, so 1/64 is 0.015625, 1/32 is twice that, 1/16 twice again. If a result does not follow that doubling you have almost certainly typed the wrong denominator.
Sixty-Fourths Handled Exactly
Every denominator on a standard imperial rule — halves through 64ths — divides out cleanly, so 27/64 returns 0.421875 with no residue in the last digit.
Six Decimal Places of Inch
Results are carried to six places, which is three digits past the tenth-thousandth a shop caliper can resolve — nothing useful is lost on the way to your setup sheet.
Digits-and-Slash Entry Guard
The input refuses any key that is not a digit or a slash, so gloved fingers and shop keyboards cannot sneak a stray character into a dimension.
Hands the Value Back to the Rule
The arrow button opens the decimal-to-fraction page with the current decimal already loaded, so a caliper number becomes a tape-measure mark in one click.
Workshop Questions About Fractional Inches
How many decimal places does the result carry?
Six. The value is rounded to the millionth of an inch and any trailing zeros are trimmed, so 1/2 shows as 0.5 rather than 0.500000. For fractions whose denominator is a power of two the six places are exact — 1/64 really is 0.015625 and nothing is being hidden. For thirds and sevenths the sixth place is a rounded digit: 1/3 displays as 0.333333 and 2/3 as 0.666667, rounded up in the last place.
Does it recognise 64ths, or only 16ths and 32nds?
Every denominator you can type is divided out directly, so 64ths, 100ths and anything else all convert. The imperial ladder that matters in a shop — 2, 4, 8, 16, 32 and 64 — is covered end to end. Where the tool is picky is the return trip: the reverse page rebuilds fractions from a fixed ladder that tops out at 64ths, so a 128th of an inch will not come back cleanly in that direction.
What happens with a top-heavy fraction like 11/8?
It converts exactly as written: 11 ÷ 8 = 1.375 in. Nothing objects to a numerator larger than the denominator, which is convenient because top-heavy form is the only way to enter a measurement over one inch on this page. A board marked 2¼ in becomes 9/4 and reads back as 2.25.
Why will the space bar not work in the fraction box?
The field filters keystrokes down to digits and the slash so that a half-pressed key cannot quietly change a dimension, and the space bar falls outside that set. Pasting still works if you already have 1 1/2 on the clipboard, but typing it is deliberately blocked. Converting the whole number into the numerator first is faster anyway: multiply the whole part by the denominator and add the top number, so 1½ becomes 3/2.
Should I round 0.4375 before typing it into CAD?
Paste the full figure and let the software round for display. Fractions of an inch with a power-of-two denominator terminate, so 0.4375 is the complete number, not a truncation — rounding it to 0.44 by hand throws away seven thousandths for no reason. Rounding is only a real decision for repeating results such as 0.333333, and even then it belongs at the end of the calculation rather than at the point of entry.
No comments yet. Be the first to comment!