How to measure a roof for shingles: square footage, pitch and bundles

How to calculate roof square footage, and why the footprint is the wrong number

Roof square footage is the plan area times the pitch factor, and every shingle count starts with that one multiplication. Take the roof's shadow on the ground at noon, which roofers call the plan or projected area, and multiply it by the pitch factor. The plan area is the footprint of the walls plus the overhang on every side. The pitch factor is the length of a rafter divided by the horizontal distance it covers, and Pythagoras gives it directly: √(1 + (rise ÷ 12)²).

The house used on this page is 44 ft by 30 ft at the walls, 1,320 sq ft. The eaves stick out 12 in all around, so the roof's shadow is 46 ft by 32 ft, 1,472 sq ft. At a 6/12 pitch the factor is 1.1180, and the roof surface is 1,645.7 sq ft. That is 24.7% more than the footprint the tax card shows.

Roofing is priced and sold by the square, which is 100 sq ft of roof surface. This roof is 16.46 squares before any waste.

On a roof where every face has the same pitch, the shape does not change the area. The same 46 ft by 32 ft outline at 6/12 is 1,645.7 sq ft as a gable and 1,645.7 sq ft as a hip. What the shape changes is the waste and the linear footage of ridge, hips and edges, and both of those change the order.

Roof pitch factor table: pitch, degrees and multiplier

Find your pitch in the first column and multiply your plan area by the pitch factor. These values come out of the same function the roofing calculator uses, so the two will always agree. The last column is the sloped surface you get for every 1,000 sq ft of plan area.

Two code limits sit at the bottom of this table. IRC R905.2.2 allows asphalt shingles only on slopes of 2/12 or steeper, and between 2/12 and 4/12 it requires a double layer of underlayment. If your measurement lands below 2/12, shingles are off the list, and the order you are building is for a different material.

Tools and what they cost

You need less than you think. A 25 ft tape measure covers the walls and the overhang. A 100 ft tape saves time on long walls but a 25 ft tape and a helper do the same job. For pitch, a level of 24 in or longer and a tape work in the attic. A magnetic angle locator, $11.99 at Menards on 2026-09-19, reads the angle straight off a rafter or a rake board and saves the arithmetic. A digital angle gauge was $29.97 the same day; for this job it adds nothing the $11.99 dial does not.

For a satellite outline, free mapping software with a polygon or area tool is enough. For a roof walk you need a ladder long enough to extend 3 ft above the eave, which is the OSHA rule for workers, and fall protection. If you don't have both, stay on the ground. You lose nothing in accuracy.

Step by step: measuring from the ground, the attic and the air

The declared case for the rest of this page: a 44 ft by 30 ft house, 12 in overhangs, a hip roof at 6/12, one plumbing vent and one bath fan through the roof.

1. Measure the walls. Run the tape along each wall at the foundation or the siding, corner to corner. Write the four sides down separately.

   Check: opposite walls should agree within about an inch. If they don't, you measured around a bump-out or a chimney chase; sketch it and measure it as its own rectangle.

2. Measure the overhang. Stand under the eave and measure from the wall straight out to the face of the fascia board. Do this on an eave and on a gable end if the house has one, because rake overhangs are often shorter than eave overhangs.

   Check: the gutter doesn't count. Measure to the fascia, and add the overhang twice to each dimension. Here 44 + 2 = 46 ft and 30 + 2 = 32 ft, a plan area of 1,472 sq ft.

3. Find the pitch in the attic. Hold a level horizontal with one end touching the underside of a rafter. Mark 12 in along the level from that end. Measure straight up from the mark to the bottom of the rafter. That measurement in inches is the rise per foot. Six inches means 6/12. With an angle locator, set it on the side of the rafter and read the degrees, then find the pitch in the table above.

   Check: repeat on a second rafter on another face. Readings within 1/4 in of each other are good. The error is small either way: reading 6 1/4 in instead of 6 in changes the factor from 1.1180 to 1.1275, under 1% of area.

4. Multiply. 1,472 sq ft × 1.1180 = 1,645.7 sq ft of roof surface, 16.46 squares.

   Check: if any face has a different pitch, such as a porch roof at 3/12, measure its plan area separately and use its own factor.

5. Cross-check from the air. Open a satellite view of the house, trace the roof outline with the area tool and compare it with your plan area. The photo sees the roof from above, so it includes the overhangs and shows the plan area directly. It does not know the pitch.

   Check: if the aerial plan area and your 1,472 sq ft disagree by more than a few percent, something was missed, usually a porch roof, a bay or an overhang measured short.

6. If you walk the roof, measure faces instead. On the roof, the tape reads the sloped length directly and you don't need the factor. The hip roof here has two trapezoids and two triangles. Each long face is (46 + 14) ÷ 2 × 17.89 ft = 536.7 sq ft; each end triangle is 32 × 17.89 ÷ 2 = 286.2 sq ft. The four add up to 1,645.7 sq ft, the same number the formula gave from the ground.

   Check: the 17.89 ft is the slope distance from the eave to the ridge, measured square to the eave. Measuring along a hip instead gives 24.0 ft, and using that number inflates the area.

How much waste to add for shingles, by roof shape

Add from 8% on a shed roof to 18% on an L or T with valleys. Area is what the shingles cover. The order is area plus the pieces that get cut off at rakes, hips, valleys and anything poking through the roof. A flat 10% for everything overbuys on a shed roof and underbuys on a cut-up one. The calculator on this site sets the starting waste by shape and adds one point per penetration:

The house here is a hip with two penetrations: 15% + 2% = 17%. The order area is 1,645.7 × 1.17 = 1,925.5 sq ft, 19.26 squares. The same house as a gable would carry 12% and need 1,843.2 sq ft. Your crew's habits matter too; these are starting points, and the calculator lets you change them.

How many bundles of shingles do you need? Squares to bundles

Divide the order area by the coverage per bundle, about 33 sq ft, and round up once at the end. Most architectural shingles are sold 3 bundles to the square, and the nominal square is 100 sq ft. Read the wrapper anyway. Owens Corning's Oakridge spec says 3 bundles and 64 shingles make a square, and that square covers 98.4 sq ft, so each bundle covers 32.8 sq ft. On this roof the difference is one bundle: 58 bundles at 100 sq ft a square, 59 at 32.8 sq ft a bundle. Round up once, at the end, on the bundle count.

Ridges, hips, eaves and rakes are bought by the foot, and they do not scale with area. The hip roof has four hips of 24.0 ft each, 96 ft in all, and a ridge of 14 ft. A hip is longer than it looks from below: in plan it runs 22.63 ft on the diagonal from the corner to the end of the ridge, and it also climbs the 8 ft the ridge sits above the eave. Hips and ridge take the same cap shingle, so this roof needs 110 ft of cap.

Valleys are the other linear item, and this roof has none. Put a 14 ft wing on the back of the same house and the calculator finds two valleys totaling 48 ft, the waste goes to 18% plus penetrations, and the order jumps to 80 bundles of Oakridge for 2,182.4 sq ft of roof. IRC R905.2.8.2 requires the valley lining to go down before the shingles, following the shingle maker's instructions.

The material list for the example roof

A hip roof has no rakes, so the starter runs only along the 156 ft of eave. Owens Corning's instructions ask for six nails per shingle for the maximum wind warranty, which makes 7,395 nails and a second box. IRC R905.2.6 sets four as the floor. Ice barrier, vents and pipe boots depend on your climate and your attic, and the roof replacement cost guide works through them line by line with labor, disposal and a permit.

Mistakes that cost money

Every one of these produces a plausible number that is wrong. They only show up on the roof, when the crew runs out.

The most common one is using the footprint with no overhang. On this house, skipping the 12 in overhangs gives 1,475.8 sq ft of roof and 53 bundles instead of 59. Six bundles short is $269.82 in shingles, plus a second delivery and a crew standing around waiting for it.

Forgetting the pitch factor does the same damage. Taking the 1,472 sq ft plan area as the roof area also lands on 53 bundles. Same $269.82 shortfall. On a 10/12 roof the same mistake misses 23% of the surface.

Counting only the ridge for cap shingles is the hip-roof trap. The ridge is 14 ft, which is one bundle of cap. The hips are another 96 ft. Order one bundle when you need four and you are $250.44 short in cap.

Using gable waste on a hip, 12% instead of 17%, gives 57 bundles. That is two short, $89.94.

Measuring along the hip for area runs the other way. Using the 24.0 ft hip length in place of the 17.89 ft slope overstates every face by 34%, and you pay for shingles that go back to the store, if the store takes them.

Overbuying one bundle is cheap insurance at $44.97. Ask the supplier about returns on unopened bundles before you order.

Measure it yourself or let the roofer do it

Measuring costs you an hour or two and, at most, an $11.99 angle locator. The roofer's version costs about $64.43 for each hour of a roofer's time, and here is how that number is built. The BLS put the national mean roofer wage at $27.95 an hour in May 2025, with half of the 135,490 roofers earning less than $26.65. Construction employers pay $51.96 in total compensation for every $36.13 of wages, so an hour costs the company $40.20. Roofing contractors, by the 2022 Economic Census figures worked out in the replacement guide, carry overhead and profit of 60.3% on top of direct cost. That makes $64.43.

If the roofer measures as part of a quote, the measurement costs you nothing either way. The reason to do it yourself is to check the quote. At the $620 a square that the replacement guide found for a typical tear-off in 2026, every square a quote overstates is money you pay for shingles nobody installs. On this roof, ask for two numbers: squares of roof (16.46) and squares ordered with waste (19.26). A quote that gives only one round number hides both.

To run your own house, enter the footprint, the overhang and the pitch in the roofing calculator. It uses the same geometry as this page, so its squares, bundles, hips and valleys will match the numbers you just worked out by hand. If the numbers point to a leak you need to handle first, the roof leak repair guide covers that, and if you are weighing steel over shingles, see how to install a metal roof.