Tape Measure Fraction Calculator
Type measurements the way you read them off a tape, such as 3 7/16 or 5' 3 1/2".
Your measurements
Type measurements the way you read them off a tape. The answer updates as you type.
What do you want to do?
Two measurements
Read as 3 7/16" (3.4375 in).
Read as 5 3/8" (5.375 in).
Tape measure precision
The answer is rounded to the nearest mark at this precision. 1/16 is the usual tape; 1/32 and 1/64 are for machinist and fine work.
What can I type?
- 3 7/16 or 3-7/16 (inches and a fraction)
- 7/16 or 3.4375 (a fraction or a decimal)
- 5' 3 1/2" or 5ft 3in (feet and inches)
- 5-3 1/2 (feet, then inches with a fraction)
Results
A + B, to the nearest 1/16
= 8.8125 in exactly
3 7/16 + 5 3/8 lands exactly on a 1/16 mark.
- Exact decimal
- 8.8125in
- Millimetres
- 223.84mm
- Feet and inches
- 8 13/16"
- Rounding error
- None
Nearest mark at each precision
The same answer on a 1/8, 1/16, 1/32 and 1/64 tape.
Nearest mark at each precision
The same answer on a 1/8, 1/16, 1/32 and 1/64 tape.
| Tape | Nearest mark | Error (in) |
|---|---|---|
| 1/8 | 8 7/8" | +0.0625 |
| 1/16 | 8 13/16" | 0 |
| 1/32 | 8 13/16" | 0 |
| 1/64 | 8 13/16" | 0 |
How this was calculated
Each step, with your numbers.
How this was calculated
Each step, with your numbers.
Step 1: Turn A and B into decimal inches
whole + numerator ÷ denominator
= A = 3 7/16 = 3.4375 in; B = 5 3/8 = 5.375 in
= 3.4375 in and 5.375 inA fraction is its top number divided by its bottom number: 7/16 is 7 ÷ 16 = 0.4375. Feet are multiplied by 12 first.
Step 2: Do the arithmetic in decimals
A + B
= 3.4375 + 5.375
= 8.8125 inWorking in decimals is exact; the rounding to a tape mark only happens at the end. That is the step that is easy to get wrong by hand with unlike fractions.
Step 3: Round to the nearest 1/16
round(inches × 16) ÷ 16
= round(8.8125 × 16) ÷ 16
= 8 13/16"The answer lands exactly on a 1/16 mark, so there is no rounding error.
Step 4: Convert to millimetres
inches × 25.4
= 8.8125 × 25.4
= 223.84 mmOne inch is exactly 25.4 mm. The millimetre figure is for the exact answer, not the rounded mark.
In short
3 7/16 + 5 3/8 = 8 13/16" (exactly 8.8125 in, 223.84 mm). Fractions are added as decimals, then rounded to the nearest 1/16.
Get the answer as the nearest tape mark, in decimals and in millimetres, or split a length into equal parts.
Sixteenths of an inch as decimals and millimetres
Exact conversions: each decimal is the fraction divided out, and each millimetre value is the decimal times 25.4.
| Fraction of an inch | Decimal inches | Millimetres |
|---|---|---|
| 1/16 | 0.0625 | 1.59 |
| 1/8 | 0.125 | 3.18 |
| 3/16 | 0.1875 | 4.76 |
| 1/4 | 0.25 | 6.35 |
| 5/16 | 0.3125 | 7.94 |
| 3/8 | 0.375 | 9.52 |
| 7/16 | 0.4375 | 11.11 |
| 1/2 | 0.5 | 12.7 |
| 9/16 | 0.5625 | 14.29 |
| 5/8 | 0.625 | 15.88 |
| 11/16 | 0.6875 | 17.46 |
| 3/4 | 0.75 | 19.05 |
| 13/16 | 0.8125 | 20.64 |
| 7/8 | 0.875 | 22.23 |
| 15/16 | 0.9375 | 23.81 |
Worked example: 3 7/16 + 5 3/8
Two measurements added and shown to the nearest 1/16.
Step 1: Turn A and B into decimal inches
whole + numerator ÷ denominator
= A = 3 7/16 = 3.4375 in; B = 5 3/8 = 5.375 in
= 3.4375 in and 5.375 inA fraction is its top number divided by its bottom number: 7/16 is 7 ÷ 16 = 0.4375. Feet are multiplied by 12 first.
Step 2: Do the arithmetic in decimals
A + B
= 3.4375 + 5.375
= 8.8125 inWorking in decimals is exact; the rounding to a tape mark only happens at the end. That is the step that is easy to get wrong by hand with unlike fractions.
Step 3: Round to the nearest 1/16
round(inches × 16) ÷ 16
= round(8.8125 × 16) ÷ 16
= 8 13/16"The answer lands exactly on a 1/16 mark, so there is no rounding error.
Step 4: Convert to millimetres
inches × 25.4
= 8.8125 × 25.4
= 223.84 mmOne inch is exactly 25.4 mm. The millimetre figure is for the exact answer, not the rounded mark.
Before you mark
- Mark every point from the same end of the board. Stepping a rounded part size along the tape adds the rounding error up.
- Cutting a board into parts removes a saw kerf at each cut. This tool divides the length itself, so take the kerf off the parts if the pieces must come out equal.
- A rounded answer can be a hair off. If two parts must match, measure one and copy it with a stop block or a marked stick rather than measuring each.
- The grammar is small on purpose: inches with a fraction or decimal, feet and inches with ' and " or ft and in, and 5-3 1/2. If your entry is refused, the message says what to change.
Tape measure fractions: common questions
Formats, rounding and equal parts.
How do you add fractions on a tape measure?
Turn each measurement into a decimal, add, then round to the nearest mark on your tape. 3 7/16 is 3.4375 and 5 3/8 is 5.375, so the sum is 8.8125, which is 8 13/16. By hand you would first rewrite 3/8 as 6/16 so both fractions have the same bottom number; the calculator does this by working in decimals.
What can I type into the boxes?
Inches as 3 7/16, 3-7/16, 7/16 or 3.4375, and feet and inches as 5' 3 1/2", 5ft 3in or 5-3 1/2. The form 5-3 1/2 is read as 5 feet 3 1/2 inches, while 3-7/16 is read as 3 and 7/16 inches. Anything that could mean two things, such as 5 3 or 5-3, is refused instead of guessed. For multiply and divide, B is a plain number such as 2 or 1/2.
Why is the answer rounded, and by how much?
A tape only has marks every 1/8, 1/16, 1/32 or 1/64 inch, so the answer is shown at the nearest mark you choose. The exact decimal is shown too, and the rounding error is the gap between the two. At 1/16 the error can be up to 1/32 inch, about 0.8 mm. Pick a finer precision if that matters for the joint.
How do I divide a length into equal parts?
Use the Divide a length mode. Enter the length and the number of parts. For N parts you need N − 1 marks, each worked out from the exact distance from one end and then rounded to a tape mark. Measuring every mark from the same end avoids adding up the rounding error. This divides the length itself; it does not allow for saw kerf if you cut the parts apart.