Shed Roof & Lean-To Calculator
Calculate rafter lengths, roof pitch angle, 4x8 plywood sheathing sheets, and roofing squares for lean-to shed roofs.
Input Parameters
Enter dimensions and specifications to estimate materials.
Rafters Needed
Board Length to Buy
15ft
Exact Rafter Length
177.1in
Roof Slope Angle
18.4°
Roof Area
265.6sq ft
Sheathing (4' x 8' sheets)
10sheets
Roofing Squares
2.7squares
Fascia
66linear ft
Material estimates include recommended trade waste buffer. Always confirm dimensions on site prior to ordering.
How The Calculation Works
Formulas, material coverage assumptions, waste buffers, and rounding standards.
Rafter length is the hypotenuse of the run and rise given by the pitch, plus the overhang. The figure is then rounded up to the next stock lumber length, since you cannot buy a 10 ft 4 in board.
Rafter count follows from the shed length divided by the on-centre spacing, plus one for the final rafter at the end wall.
Sheathing is counted in 4' x 8' sheets against the sloped area, not the footprint — the same pitch correction that catches people out on full roofs applies here.
You May Also Need
Common complementary tools used alongside this calculator for complete project estimation.
Roofing Shingle Calculator
Calculate roof squares, asphalt shingle bundles, and waste percentages adjusted for roof pitch multipliers.
Gutter Length & Downspout Calculator
Calculate linear feet of 5" or 6" rain gutters, downspouts (1 per 35ft rule), end caps, corners, and fascia hangers.
Siding & Squares Calculator
Calculate siding squares (100 sq ft), vinyl lap panels, starter strips, and J-channel molding with window deductions.
Insulation Batts & Rolls Calculator
Calculate insulation rolls and batts needed for walls, attics, and crawlspaces across R-13, R-19, R-30, R-38, and R-49 ratings.
Attic Ventilation & Ridge Vent Calculator
Calculate Net Free Vent Area (NFVA) under the 1:300 code rule, continuous ridge vent footage, and soffit intake vents.
HVAC BTU & AC Tonnage Sizing Calculator
Estimate room heating and cooling BTU requirements and AC tonnage adjusted for ceiling height, climate zone, and insulation.
Frequently Asked Questions
Practical installation guidance and purchasing tips for shed roof & lean-to calculator.