Roofing Calculator
Calculate roof area, shingles, bundles, underlayment rolls, and ridge cap pieces based on roof pitch. Includes waste percentage and cost estimates.
Roof details
Updates as you typeMode
What do you want to solve for? ?
Budget ?
—
$
Bundles on hand ?
—
bundles
Roof shape
Shape ?
Material
Roofing material ?
Footprint
Length ?
ft
Width ?
—
ft
Roof pitch
Pitch ?
—
Waste & cost
Waste % ?
—
%
Material cost ?
—
$
/ sq ft
Labor ?
—
$
/ sq
Tear-off & disposal ?
Display (optional)
Currency
Formula
A
=
L
×
W
×
mpitch
×
mshape
×
(
1
+
w
)
- A
- Total roof surface you need to order
- L × W
- Ground-level footprint of the building
- mpitch
- Pitch multiplier — √(1 + (rise/run)²). A 4/12 roof = 1.054; a 12/12 roof = 1.414.
- mshape
- Shape multiplier. Gable / hip / shed = 1.00; L-shape adds 8% for the valley.
- w
- Waste allowance (as a decimal) for cuts, mistakes, and spares
Worked example — your numbers
- Footprint L × W = —
- Pitch multiplier mpitch = —
- Shape multiplier mshape = —
- Roof surface = —
- With waste (—) = —
- Material units = —
Pitch-multiplier reference
| Pitch | Multiplier | Angle | Feel |
|---|---|---|---|
| 1/12 | 1.003 | 4.8° | Nearly flat |
| 2/12 | 1.014 | 9.5° | Low slope |
| 3/12 | 1.031 | 14.0° | Low slope |
| 4/12 | 1.054 | 18.4° | Low / standard (walkable) |
| 5/12 | 1.083 | 22.6° | Standard (walkable) |
| 6/12 | 1.118 | 26.6° | Standard (walkable) |
| 7/12 | 1.158 | 30.3° | Steep |
| 8/12 | 1.202 | 33.7° | Steep |
| 9/12 | 1.250 | 36.9° | Steep |
| 10/12 | 1.302 | 39.8° | Very steep |
| 11/12 | 1.357 | 42.5° | Very steep |
| 12/12 | 1.414 | 45.0° | Very steep |
We assume 3 shingle bundles per 100 sq ft square, 400 sq ft per underlayment roll, and 3 ft per ridge-cap piece. Metal panels, standing seam, and tile swap the primary unit but keep the same area math. The shape multiplier is a rough adjustment — a building with many valleys, dormers, or irregular wings will generate more waste in practice.