Framing & Carpentry

Stairs, rafters, board feet, square — the daily four.

Stair Stringer

Total rise → even risers + total run. Aim ~7–7¾″ risers, ~10–11″ treads.

Total rise (finished floor to floor)

Target riser

Tread depth

Risers

7.714" each

Total run

136.5"

13 treads

Keep every riser within ⅜″ of each other. Verify riser/tread limits for your local residential code.

Rise-over-12 pitch → rafter length per run (before ridge & overhang).

Pitch (rise per 12)

/12

Horizontal run

Rafter length

13.42 ft

6/12 · ×1.118/ft

Slope angle

26.6°

off horizontal

Add for ridge thickness (½) and your overhang/tail, then cut the plumb & seat.

Order lumber by volume: thickness × width × length ÷ 12.

Thickness

Width

Length

Pieces

pcs

Total board feet

80 bf

nominal dimensions

Two legs → hypotenuse + angles. The 3-4-5 check, any size.

Leg A

Leg B

Hypotenuse (diagonal)5

Angle at A / B36.9° / 53.1°

3-4-5: measure 3 one way, 4 the other — diagonal is 5 when it's square. Scale it (6-8-10, 9-12-15) for longer walls.
Stairs: risers = total rise ÷ ~7.5, rounded. Actual riser = total rise ÷ risers. Treads = risers − 1.
Rafter/ft of run: √(rise² + 12²) ÷ 12. A 6/12 is ×1.118; 12/12 is ×1.414.
Board foot: (T″ × W″ × L′) ÷ 12. A 2×6×8 = 8 bf.
Common studs: 16″ O.C. → studs ≈ (wall length ÷ 16) + 1, plus plates & openings.