How to measure a roof for shingles from the ground (worked example)
· 7 min read
You do not need to climb on the roof to order shingles for it. Two measurements on the ground, the pitch from the attic, and the arithmetic is four lines: plan area, times the pitch multiplier, divided by 100 for squares, plus waste, times three for bundles. This is that arithmetic on one house, 30 x 40 ft with 1 ft of overhang at 6:12, worked through to 50 bundles, 2 rolls of underlayment, 2 bundles of ridge cap, 3,847 nails and 16 pieces of drip edge, and then the same house as a hip roof and at four pitches.
Roof shingle calculatorRoof pitch calculator
Step 1: the plan, on the ground
Walk the two sides of the house with a tape: the length along the ridge and the width from eave to eave. Then add the overhang, the part of the roof that sticks out past the walls, on every side; a tape held up to the eave from a ladder gives it; the example uses 1 ft. The example house has 30 x 40 ft of walls and 1 ft of overhang, so the roof plan is 32 x 42 ft: 1,344 sq ft. That plan area is what every other number hangs off, and it is the number people get wrong by using the floor area of the house instead.
Step 2: the pitch
The roof surface is bigger than its plan because it slopes. Pitch is the rise per 12 in of run: in the attic, hold a level against a rafter, mark 12 in along the level from where it touches, and measure up from the mark to the rafter. Six inches is 6:12, which is 26.6° and a multiplier of 1.118(the square root of 1 + (6 / 12)²). The roof pitch calculator turns degrees or any rise and run into the multiplier, and the roof pitch guide has the chart from 1:12 to 12:12.
Step 3: squares, waste and bundles
Roof area = 1,344 x 1.118 = 1,503 sq ft. A roofing square is 100 sq ft, so that is 15.03 squares of roof. Add 10% for the cuts at the rakes and around vents on a simple gable (IKO, Blueprint for Roofing, read 2026-09-20): 16.53 squares to order. Standard 3-tab and architectural shingles are packed 3 bundles to the square (Owens Corning, Section 07 31 13 specification guide, 2013, TruDefinition Oakridge shingles, read 2026-09-20), so 16.53 x 3 = 49.59, rounded up to 50 bundles. The bundles per square guide explains the rule and the heavier shingles that take 4 or 5 bundles.
Step 4: the rest of the order
The same plan gives the lengths of the edges. On a gable the ridge is the length of the plan, 42 ft; the eaves are the two long edges and the rakes the two gable ends measured along the slope, 155.6 ft of drip edge altogether. Underlayment is squares to order divided by the roll: 10 squares per synthetic roll (Owens Corning, Section 07 31 13 specification guide, 2013, Deck Defense synthetic underlayment, read 2026-09-20). Ridge cap comes in 25 ft bundles (Superarbor, GAF Seal-A-Ridge hip and ridge cap shingles, read 2026-09-20), nails at 4 per shingle and 64 shingles per square, weighed at 185 to the pound (Fastener USA, "How to Calculate How Many Roofing Nails You Need", 9 February 2023, 1-1/2 in roofing nails, read 2026-09-20), drip edge in 10 ft pieces. The table has the gable next to the same house as a hip roof: same area, 15% waste instead of 10%, a short ridge plus four hips to cap, eaves all round and no rakes.
| Item | Gable | Hip |
|---|---|---|
| Plan area (sq ft) | 1,344 | 1,344 |
| Roof area (sq ft) | 1,503 | 1,503 |
| Squares | 15.03 | 15.03 |
| Waste | 10% | 15% |
| Squares to order | 16.53 | 17.28 |
| Bundles | 50 | 52 |
| Underlayment (rolls) | 2 | 2 |
| Ridge and hips (ft) | 42 | 106 |
| Ridge cap (bundles) | 2 | 5 |
| Nails | 3,847 | 3,847 |
| Nails (lb) | 20.8 | 20.8 |
| Eaves and rakes (ft) | 155.6 | 148 |
| Drip edge (pieces) | 16 | 15 |
| Installed cost | $6,011 to $9,016 | $6,011 to $9,016 |
Step 5: what it costs
Installed cost = squares of roof x the price per square, without the waste (the roofer buys the extra bundles inside an installed price). The calculator starts from the HomeAdvisor, "How Much Does a Roof Replacement Cost?", updated 17 June 2026, table "Roofing Material | Average Cost", read 2026-09-20 range for architectural shingles, $400 to $600 per square, so the example house is $6,011 to $9,016; a quote from a local roofer replaces it, and the new roof cost guide has every material on a 1,500 sq ft footprint. Tear-off, decking and flashing are quoted on top.
The same house at four pitches
Everything but the pitch held: the steeper the roof, the more surface on the same plan. From 4:12 to 10:12 the example house gains 333 sq ft of roof and 11 bundles.
| Pitch | Multiplier | Roof area (sq ft) | Squares | Bundles | Installed cost |
|---|---|---|---|---|---|
| 4:12 | 1.054 | 1,417 | 14.17 | 47 | $5,667 to $8,500 |
| 6:12 | 1.118 | 1,503 | 15.03 | 50 | $6,011 to $9,016 |
| 8:12 | 1.202 | 1,615 | 16.15 | 54 | $6,461 to $9,692 |
| 10:12 | 1.302 | 1,749 | 17.49 | 58 | $6,998 to $10,497 |
Then let the calculator carry it
Type the width, length, overhang, pitch and shape of each section into the roof shingle calculator and it repeats these steps for all of them together, with the waste, roll and bundle figures editable and their sources shown. For a shed the shed chart already has 8 x 8 to 12 x 16 ft worked out. The Pro materials list prints the whole order, section by section, and exports it to Excel with the formulas in the cells.
Frequently asked questions
- Do I measure the house or the roof?
- The roof: the plan of the roof seen from above, which is the walls plus the overhang on every side. On the example house the walls are 30 x 40 ft and the roof plan is 32 x 42 ft, 1,344 sq ft. The floor area of a two-storey house is about twice its footprint, so never start from the square footage in the listing.
- How do I find the pitch without going on the roof?
- In the attic, hold a level against the underside of a rafter, mark 12 in along it from the point of contact and measure straight up to the rafter: that many inches is the pitch in x:12. From the ground, count courses of siding on the gable end for the rise and the run, or lay a phone inclinometer on the slope from a ladder for the degrees. 6:12 is 26.6° and a multiplier of 1.118; the roof pitch calculator converts any of the three into the others.
- How much waste should I add for shingles?
- 10% on a simple gable and 15% on a hip roof or one with valleys (IKO, Blueprint for Roofing, read 2026-09-20), applied to the squares before the bundles are rounded up. On the example house that is 16.53 squares to order as a gable and 17.28 as a hip, 50 and 52 bundles. Dormers, chimneys and a cut-up plan push it up; type your own figure in the calculator.
- What if my roof is not a rectangle?
- Split it into rectangles on the plan, each with its own pitch and shape, and add them: an L-shaped house is two sections, a house with a garage wing three. The calculator takes up to 12 sections and totals the area, ridge, hips and edges across all of them, so the ridge cap and drip edge come out right too.
- How many squares is a 1,344 sq ft roof plan at 6:12?
- 15.03 squares: 1,344 x 1.118 = 1,503 sq ft of roof surface, / 100. With 10% waste and 3 bundles per square that is 50 bundles; the bundles per square guide has the same chart for round footprints from 1,000 to 3,000 sq ft.
Planning quantities from manufacturer coverage figures and published cost ranges, each with its source and date: measure the roof and follow the product data sheet. Not a structural assessment.