Carpentry - Rafters and Pitch

Carpentry

Rafters and Pitch

Converting the Span of a Pitched Roof to Sqft of Roofing Surface Area

Multiply the roof's span times the pitch factor to obtain the total sloped length of the roof. The total sloped length (lnft) times the run of the roof's rafters (lnft) equals the roofing area (sqft).

Pitch factor

Flat roof                      0
½ in 12 pitch             1.00087
1                                  1.00347
1½                               1.00778
2                                  1.01379
2½                               1.02147
3                                  1.03078
3½                               1.04167
4                                  1.05409
4½                               1.06800
5                                  1.08333
5½                               1.10003
6                                  1.11803
6½                               1.13728
7                                  1.15770
7½                               1.17925
8                                  1.20185
8½                               1.22545
9                                  1.25000
9½                               1.27544
10                                1.30171
10½                             1.32877
11                                1.35657
11½                             1.38506
12                                1.41421
12½                             1.44398
13                                1.47432
13½                             1.50520
14                                1.53659
14½                             1.56846
15                                1.60078
15½                             1.63352
16                                1.66667
16½                             1.70018
17                                1.73405
17½                             1.76826
18                                1.80278