Online Calculators FreeReference Manual

Trades & Shop Calculator

Rafter lengths, roof pitch, snow load, stair layout, board feet, pipe offsets, clearance holes, and arch geometry — the trades formulas, all showing their work.

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CalculatorFORM TRADES CALCULATOR
ft
in per 12
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RESULT
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Job-site math, no guessing

Rafters, stairs, and offsets are unforgiving: wrong numbers mean cut lumber in the scrap pile. Every member here shows the exact formula and its result — the pitch multiplier for rafters, the 2×riser+tread comfort rule for stairs, the Pythagorean diagonal for pipe travel.

Where the rules come from

Pitch multipliers are pure trigonometry: √(144+rise²)/12. Stair geometry follows the IRC (max 7¾ in riser, 10 in tread) plus the 2R+T≈25 in comfort rule that codes only partly capture. Board feet is the lumberyard definition: nominal thickness × width × length ÷ 12.

Worked example

  1. A 24 ft wide garage, 6/12 pitch roof.
  2. Run = 12 ft; pitch multiplier = √(144+36)/12 = 1.118.
  3. Rafter = 12 × 1.118 = 13.42 ft, plus overhang.
  4. Roof angle reads 26.6° — conventional territory.

How to use it

  1. Pick the trade formula from the dropdown.
  2. Enter your dimensions — defaults show a typical case.
  3. Read the result, the formula, and the code note.
  4. Print or share the sheet for the job site.

Frequently asked questions

How do I calculate rafter length?

Multiply the horizontal run by the pitch multiplier √(144+rise²)/12. A 6/12 pitch multiplies by 1.118; add the overhang to the run before multiplying for the real-world length.

What is the 2R+T rule for stairs?

Twice the riser plus the tread should land near 24–25 inches — the comfortable stride. Codes separately cap risers (7¾ in residential) and set minimum tread (10 in).

How many board feet is a 2×6×10?

2 × 6 × 10 ÷ 12 = 10 board feet per board. Multiply by your board count; the member prices it at any rate you enter.

What snow density should I use?

Fresh powder runs about 7 lb/ft³, settled snow 10–15, wet or packed 20–30. Structural design uses the ASCE 7 map for your county instead.

What is a rolling offset?

The diagonal pipe travel when the line shifts both across (offset) and up/down (advance): travel = √(offset² + advance²). With 45° fittings, each fitting setback is travel × 0.7071.

Does the clearance-hole chart match machinery’s handbook?

It uses the two classic conventions — close fit (bolt + 1/64") and free fit (bolt + 1/32") — which match the common chart for fractional bolts up to 1 inch.