Inch Fraction Calculator
Add, subtract, multiply, and divide mixed inch fractions like 3 5/8" + 4 7/16". Auto-reduces to lowest terms, snaps to your chosen precision (1/2" through 1/64"), and shows decimal inches plus millimeters for every result. Built for carpenters, woodworkers, cabinetmakers, and machinists.
Fraction Inputs
Lumber Actual Widths
Tap to load actual (planed) dimensions into Input A or B.
Common Woodworking Fractions
Enter fractions, pick an operation, and click Calculate.
Inch Fraction to Decimal to Millimeter Reference
A quick-lookup chart of the 16 sixteenth-inch increments most commonly found on a US tape measure. Print this out for your shop, or bookmark it for the jobsite.
| Fraction | Decimal Inches | Millimeters |
|---|---|---|
| 1/16" | 0.0625 | 1.59 mm |
| 1/8" | 0.125 | 3.18 mm |
| 3/16" | 0.1875 | 4.76 mm |
| 1/4" | 0.25 | 6.35 mm |
| 5/16" | 0.3125 | 7.94 mm |
| 3/8" | 0.375 | 9.53 mm |
| 7/16" | 0.4375 | 11.11 mm |
| 1/2" | 0.5 | 12.7 mm |
| 9/16" | 0.5625 | 14.29 mm |
| 5/8" | 0.625 | 15.88 mm |
| 11/16" | 0.6875 | 17.46 mm |
| 3/4" | 0.75 | 19.05 mm |
| 13/16" | 0.8125 | 20.64 mm |
| 7/8" | 0.875 | 22.23 mm |
| 15/16" | 0.9375 | 23.81 mm |
| 1" | 1 | 25.4 mm |
Understanding Inch Fractions in US Construction
Inch fractions are the working language of US construction. From the first stud you lay out on a wall plate to the last piece of crown molding you scribe against a ceiling, every measurement passes through the binary tape-measure scale of halves, quarters, eighths, sixteenths, and sometimes thirty-seconds. Unlike the metric system, which expresses everything as a single decimal value, inch fractions encode precision in their denominator: a 5/16" measurement is inherently coarser than a 5/32" measurement, and a carpenter trained to read a tape measure can spot the difference instantly. That is both the strength and the headache of the imperial system. The strength is speed: you can call out a measurement, mark it, and cut it without ever picking up a calculator. The headache is arithmetic: as soon as you need to add 3 5/8" to 4 7/16", you are no longer doing simple addition. You are computing a least common multiple (16), restating each fraction over that denominator (3 10/16 + 4 7/16), summing the numerators (17/16), and then converting an improper fraction back to a mixed number (8 1/16). This calculator does that work in a single click and, crucially, snaps the result back to the precision that matches your job. For framing, that is usually 1/16". For cabinet face frames, 1/32". For inlay work or CNC, decimal inches taken to four or five decimal places. The Diamond Grade version on this page also bridges to the metric world by showing every result in millimeters, because more and more imported hardware, hinges, and CNC tooling list dimensions in mm. One inch equals exactly 25.4 mm, so a 3/4" shelf pin works out to 19.05 mm, a 5/8" drawer slide takes 15.875 mm of clearance, and a 1 1/2" screw is essentially 38.1 mm. By keeping both unit systems visible side by side, you can move between US lumber-yard dimensions and European cabinet hardware specs without ever leaving the tool. That fluency, more than any single piece of software, is what separates a fast professional from a slow one.
How to Use the Inch Fraction Calculator
- Step 1: Enter the first measurement. Use the whole/numerator/denominator boxes, or type a measurement directly like "3 5/8", "5/8", or "3.625". The calculator parses all three formats automatically.
- Step 2: Pick the operation. Tap +, -, x, /, or mod. Add and subtract are the daily workhorses; multiply and divide solve repeated boards and equal spacing; mod returns the remainder for stud or joist layout.
- Step 3: Enter the second value. For add, subtract, and mod, fill in Input B. For multiply and divide, enter a scalar (e.g., 4 to quadruple, or 0.5 to halve). You can pull common board widths or fractions from the preset panels below the inputs.
- Step 4: Pick output precision. 1/16" for framing and rough carpentry, 1/32" for cabinet face frames and trim, 1/64" for joinery and inlay. The decimal-inch output stays at full precision regardless of your fraction setting, so CNC users can still copy the exact value.
- Step 5: Read, export, share. The result panel shows the reduced mixed-number fraction, decimal inches, millimeters, and the underlying formula. Tap Export for a plain-text report, Share for the native iOS/Android share sheet, or History to load any of your last twelve calculations.
Common Use Cases
Adding Board Lengths for Trim Runs
Calculating a continuous run of baseboard, chair rail, or crown means adding several pre-cut lengths together. Add 8 3/4" + 11 1/2" + 9 5/8" in sequence by pushing each running total back into Input A. If your run also has to fit a known wall length, use the subtract operation to find the remainder you need to cover.
Use the Feet & Inches Calculator ->Scaling Drawings and Plans
Architectural plans are usually drawn at 1/4" = 1' or 1/8" = 1'. Use multiply or divide on this calculator to scale a printed dimension up to its real-world equivalent (or down to plot it on graph paper). Pair it with our scale calculator for a scaled drawing workflow that handles both directions.
Use the Scale Calculator ->Converting Linear to Square Footage
When estimating flooring, sheathing, or drywall, you often have a width in inch fractions and a length in linear feet. Convert that width to decimal inches with this calculator, then drop the result into a square footage tool to get materials-by-area without guessing.
Use the Square Footage Calculator ->Stud and Joist Layout
Frame walls and floors live on 16" and 24" on-center spacing. Use mod to find the remainder after the last full bay, multiply by the stud count to lay out the whole wall, or divide a known wall length by your O.C. spacing to find your stud count.
Use the Framing Calculator ->Pro Tips From the Field
- Use 1/16" precision for most carpentry. A US tape measure is graduated in sixteenths, and any tighter precision than that is invisible to the pencil. Reserve 1/32" and 1/64" for cabinet work, fine joinery, and machined parts.
- Use 1/32" for cabinetmaking. Face frames, drawer fronts, and door reveals look terrible when they vary by a sixteenth, but they look great when they hold a thirty-second. Set the precision once at the start of the project and leave it there.
- Use decimal for CNC and laser. Most CAM and CAD software prefers decimal inches or millimeters. Copy the Decimal Inches output directly into Fusion 360, VCarve, or LightBurn without rounding. The fraction display is just for the human reading the cut list.
- Sketch your math twice. Even with this calculator, always sketch a quick layout on the back of the lumber receipt before you cut. Numbers lie; an eye-level sketch of two boards meeting at a joint catches the "wait, that does not fit" moments before you waste a board.
- Bridge to metric early. If you are installing European hinges, drawer slides, or any imported hardware, write the millimeter equivalent next to every fraction on your cut list. It eliminates the "is that 5/8" or 5/16"?" confusion when you are squinting at a hinge cup specification at the end of a long day.
What Builders Say
“I had been doing fraction math in my head for 18 years on the jobsite. This calculator caught two errors in my crown molding cut list on the first day I used it. The mm output is gold for the European hardware I install. Now my whole crew has it bookmarked.”
“We use 1/32" precision on face frames and the auto-reduce is exactly what I needed. The board width presets save me from typing 1 1/2" over and over. My CNC operator pulls decimal inches straight from this and pastes into VCarve.”
“The history feature is huge. I run six estimates a day, and being able to scroll back through my last dozen fraction calcs has saved me hours. Mod for stud spacing is something I did not know I needed until I had it.”
“I am self-taught and inch fractions used to terrify me. The ruler visualization made it click. Now I trust my cut list and my drawer fronts actually line up. Best free tool I have used all year.”
Love using our calculator?
Similar Calculators
More tools in the same category
Board and Batten Layout Calculator
Calculate board and batten spacing for perfect layouts
Feet and Inches Calculator
Add, subtract, and convert feet and inches measurements
Scale Calculator
Convert between different measurement scales for plans
Square Footage Calculator
Calculate room and area square footage accurately
Lumber Weight Calculator
Calculate lumber weight from species, dimensions and quantity. 17+ wood species, kiln-dried/green/pressure-treated moisture.
Cabinet Door Size Calculator
Calculate cabinet door dimensions for full overlay, partial overlay, or inset construction. Auto hinge count.
Often Used Together
Complementary tools for complete analysis
From Other Categories
Expand your calculations
Geometry and area calculations for building
Measurement unit conversions
Project cost and budget calculations
Related Articles
Dive deeper with our expert guides and tutorials related to Inch Fraction Calculator