Free · No login · Works on the job site

Every number a roof framer needs, before lunch.

Rafter lengths, stair stringers, board feet, angles, and span references — fast, accurate, and built for a phone in a tool belt, not a desk.

Start with rafters → Jump to span tables

Pitch

6/12

Angle

26.6°

Rafter / ft run

13.4"

Drag to change pitch 6/12

01 — Rafters

Common, Hip & Valley Rafter Calculator

Enter your building run and pitch to get theoretical rafter length, overhang-adjusted length, and hip/valley lengths. Measurements are to the ridge center line — subtract half the ridge thickness when cutting.

Run (ft) — half the building width

Pitch (rise per 12")

Overhang (in)

Roof angle—

Common rafter (to ridge)—

Common rafter (with overhang)—

Hip / valley (to ridge)—

Hip / valley (with overhang)—

Lengths measured along the top edge of the rafter. Doesn't account for ridge board thickness or birdsmouth seat cut — mark those on the stick before cutting.

02 — Stairs

Stair Stringer Calculator

Give it total rise and your target tread depth. It'll split the rise into even risers and lay out the stringer length. Most codes cap riser height around 7.75" — check your local code before cutting.

Total rise (in) — floor to floor

Max riser height (in)

Tread depth (in)

Number of risers—

Actual riser height—

Number of treads—

Total run—

Stringer length—

Riser + tread should land close to 17–18" (rule of thumb for a comfortable step). Adjust tread depth if it's off.

03 — Material

Board Feet & Cost Calculator

Standard formula: (thickness in inches × width in inches × length in feet) ÷ 12, per piece.

Thickness (in)

Width (in)

Length (ft)

Quantity

Price per board foot ($, optional)

Board feet per piece—

Total board feet—

Estimated cost—

04 — Angles

Pitch-to-Angle Converter

Convert between roof pitch (x/12), degrees, and percent slope — plus a quick-reference table for common speed square settings.

Pitch (rise per 12")

Angle from horizontal—

Percent slope—

Unit length factor (per ft of run)—

Pitch	2/12	4/12	6/12	8/12	10/12	12/12	16/12
Degrees	9.5°	18.4°	26.6°	33.7°	39.8°	45.0°	53.1°
Unit length /ft	12.17"	12.65"	13.42"	14.42"	15.62"	16.97"	20.0"

05 — Reference

Rafter Span Quick Reference

Approximate maximum spans for SPF No.2 rafters, 30 psf ground snow load / 20 psf live load. Reference only — actual allowable spans depend on species, grade, load, and local code. Always confirm with your building department or an engineer before framing.

Rafter spacing

Rafter Size	12" O.C.	16" O.C.	19.2" O.C.	24" O.C.
2×6	13'-5"	12'-3"	11'-6"	10'-6"
2×8	17'-9"	16'-2"	15'-2"	13'-11"
2×10	22'-8"	20'-8"	19'-4"	17'-9"
2×12	27'-7"	25'-1"	23'-7"	21'-7"