Carpenter Calculator: Ft-In

Carpenter Calculator is a feet-inch-fraction construction calculator built for the job site: a dedicated ft-in keyboard, exact fraction math, stair and rafter layout, board feet and a cut-list optimizer — 100% offline, with no ads and no account.

It handles feet and inches directly, and result rounding is included.

CORE TOOLS

✓ Dedicated ft-in-fraction keyboard — separate ft / in / fraction keys plus mm, cm, m; big glove-friendly keys with haptic feedback. Type 5 ft 3 in 3/8 and get 5' 3-3/8"
✓ Exact fraction math — every value is a true rational number, so 1/16 + 1/32 = 3/32 with zero floating-point error; mix metric freely (1 mm = exactly 5/127 in)
✓ Add, subtract, multiply and divide mixed ft-in-fraction and metric values with dimension tracking: length × length = area (sq ft), × length again = volume (cu ft + board feet)
✓ Result rounding to 1/2, 1/4, 1/8, 1/16, 1/32 or 1/64 — nearest, up or down
✓ Three live formats for every result: fraction ↔ decimal inches ↔ mm/m
✓ Paperless tape — scrolling history of every calculation; tap a line to reuse its value
✓ Board feet + lumber cost — W × T × L / 144, quantity and unit price
✓ Right triangle / roof pitch — enter any 2 of rise, run, hypotenuse, angle; slope shown as x/12
✓ Stair calculator with IRC code warnings (riser over 7-3/4", tread under 10")
✓ Square up — enter the sides and both measured diagonals: get the target diagonal, how far out of square you are, which corner to move and by how much, plus a scaled 3-4-5 check
✓ Nominal to actual lumber sizes built in — pick 2x4 and board feet uses 1-1/2" x 3-1/2" automatically, or switch back to nominal
✓ The tape now survives closing the app — your last 200 lines are still there tomorrow morning
✓ Dark mode and large, readable keys

WHY CARPENTERS CHOOSE THIS APP

• Feet-inch-fraction first — not a decimal calculator with a fraction bolted on.
• No ads, no account. Your measurements never leave the phone, and it works in the shop, on the roof or off the grid.
• Rounding and conversions are free, not a paid upgrade.
• No subscription, ever. Everything below is free today, and stays free for you.

LAYOUT AND ESTIMATING TOOLS — ALSO FREE

✓ Printable stair stringer cut diagram — shop-drawing style, export PNG/PDF
✓ Rafter calculator — common rafters with birdsmouth seat/plumb cuts, hip/valley, jack rafter list with step-down, 45° cheek cuts, with cross-section diagrams
✓ Equal spacing — balusters, fence pickets, shelves; auto-solves the fewest pieces that meet the 4" sphere rule, exact fractional gaps, on-center spacing
✓ Crown molding compound miter — spring angle 38/45/52 or custom + wall angle → miter and bevel settings
✓ Cut-list optimizer — bin-packing with kerf allowance: fewest boards, leftover per board, utilization % and kerf loss shown separately
✓ Material estimator — concrete volume with 80/60/40 lb bag counts, drywall and sheet goods, paint by coats and coverage, flooring or tile by the box, roofing squares and bundles, all with a waste allowance
✓ Equal spacing now prints a running mark-out list — every position measured from one end, edge and centre, so you pull the tape once instead of adding as you go
✓ Export tape as CSV

All results are informational. Always verify critical dimensions against the building code in force in your jurisdiction.

Recent changes:
• Stair calculations per TCVN 13967:2024, with the Vietnamese step-cycle count.
• One tap to read any result in metric.
• Fixed wrong stair pitch and hip-roof angles.
• Fixed: “3,5” could not be entered; the cut list now survives rotation.