Roof Pitch Calculator — Common Rafter

Set pitch and lumber size — every number and diagram updates instantly.

Roof Cross-Section — 6:12 pitch · 24' span

Pitch

Rafter Lumber

Rise (M)inches per 12" of run

Run (R)inches — usually 12

Building Spanfeet — full width

Overhanginches — eave extension

Pitch & Rafter Length

Pitch Ratio

6:12

Pitch Angle

26.6°

Slope %

50%

Line Length

—

plate to ridge

+ Overhang

—

full rafter length

Multiplier

1.118

for roof area calc

Cut Angles — Common Rafter

Plumb Cut (A)

26.6°

ridge end — set bevel from vertical

Level Cut

63.4°

seat cut — from horizontal

Total Rise

6' 0"

wall plate to ridge

Birdsmouth — 2×8 on Double 2×4 Plate

Seat Cut Depth

1¾"

cuts into rafter bottom

Seat Cut Width

3½"

= plate width

Remaining

5½"

76% — code OK

Collar Tie (IRC R802.4.1)

Min Height from Plate

4' 0"

upper ⅓ of attic

Max Height

6' 0"

= total rise (at ridge)

Collar Tie Size

1×4 min

at max 4' o.c.

Pitch Angles

Pitch Triangle

Rafter Member — 2×8 at 6:12

Birdsmouth Cut — True Scale

All Cut Dimensions

Common Pitch Reference

Pitch	Angle	Slope	Multiplier	Plumb Cut	Level Cut	Type

Material Area

Floor Footprintft² — multiply by pitch multiplier

Actual Roof Area

—

enter footprint above

1 roofing square = 100 ft²