16 ft Span 12/12 Pitch Rafter Length: 12' 7-11/16"

Overhang	Overhang length	Total rafter	Stock length
0"	0"	11' 2-11/16"	12'
12"	1' 5"	12' 7-11/16"	14'
16"	1' 10-5/8"	13' 1-5/16"	14'
24"	2' 9-15/16"	14' 0-5/8"	16'

Overhang

Overhang length

Total rafter

Stock length

11' 2-11/16"

12'

12"

1' 5"

12' 7-11/16"

14'

16"

1' 10-5/8"

13' 1-5/16"

14'

24"

2' 9-15/16"

14' 0-5/8"

16'

Pitch	Ridge rise	Rafter length	Stock length
3/12	1' 11-13/16"	9' 2-9/16"	10'
4/12	2' 7-3/4"	9' 5-1/16"	10'
5/12	3' 3-11/16"	9' 8-3/16"	10'
6/12	3' 11-5/8"	9' 11-15/16"	10'
7/12	4' 7-9/16"	10' 4-3/16"	12'
8/12	5' 3-1/2"	10' 8-7/8"	12'
9/12	5' 11-7/16"	11' 2-1/16"	12'
10/12	6' 7-3/8"	11' 7-5/8"	12'
12/12	7' 11-1/4"	12' 7-11/16"	14'

Pitch

Ridge rise

Rafter length

Stock length

3/12

1' 11-13/16"

9' 2-9/16"

10'

4/12

2' 7-3/4"

9' 5-1/16"

10'

5/12

3' 3-11/16"

9' 8-3/16"

10'

6/12

3' 11-5/8"

9' 11-15/16"

10'

7/12

4' 7-9/16"

10' 4-3/16"

12'

8/12

5' 3-1/2"

10' 8-7/8"

12'

9/12

5' 11-7/16"

11' 2-1/16"

12'

10/12

6' 7-3/8"

11' 7-5/8"

12'

12/12

7' 11-1/4"

12' 7-11/16"

14'

How the math works

Run = span ÷ 2 − ½ ridge (1-1/2"): 96" − 3/4" = 7' 11-1/4"
Slope factor for 12/12 = √(144 + 144) ÷ 12 = 1.4142
Line length = 95.250" × 1.4142 = 11' 2-11/16"
Overhang = 12" × 1.4142 = 1' 5"
Total = 12' 7-11/16" → next stock length 14'

Rafter size (2x6 / 2x8 / 2x10 / 2x12) depends on spacing, species and snow load — check the IRC rafter span tables (Section R802) for your run.

Trade pro tips

The horizontal run for this roof is 7' 11-1/4" — that is the number to look up in the IRC rafter span tables.
Cut one pattern rafter, test it at both ends of the building, then use it to mark the rest.
Measure line length along the top edge from the ridge plumb cut to the birdsmouth heel.

Frequently asked questions

How long are the rafters for a 16 ft span with a 12/12 pitch?

11' 2-11/16" from ridge to wall line, 12' 7-11/16" including a 12" overhang (1-1/2" ridge board deducted). Buy 14' boards.

How tall is a 12/12 roof on a 16 ft wide building?

The ridge rises 7' 11-1/4" above the top of the wall plate (run 7' 11-1/4" × 12/12), not counting rafter depth.

What are the rafter cut angles for 12/12?

Plumb cut (ridge and tail) 45.0°, seat cut of the birdsmouth 45.0°. On a speed square, pivot to "12" on the common scale.

How many rafters for a 16 ft wide roof?

Two per rafter pair (one each side). Pairs = building length × 12 ÷ spacing + 1 — a 20 ft long 16' wide building at 16" OC takes 16 pairs (32 rafters) of 14' stock.

16 ft Span, 12/12 Pitch Rafter Length

Quick answer

▍Rafter Length Calculator

16' span @ 12/12 — overhang options

16' span at other pitches (12" overhang)