How to Measure a Roof for Shingles (Without Climbing Up)

To measure a roof for shingles, measure the building footprint from the ground (length x width, including the overhangs), then multiply that footprint by the pitch multiplier for your roof slope. That gives you roof area. You do not need to get on the roof to estimate. A tape measure, a walk around the house and one multiplier will get you close enough to order materials.

Here is the whole method in one line: roof area = footprint x pitch multiplier. Everything below is just how to get those two numbers, and what to do with the answer. If you want the math done for you, the Roofing Calculator takes length, width and pitch and returns roof area and squares.

Can you measure a roof from the ground?

Yes, and it is the method we recommend. The footprint of your roof is the same rectangle as the footprint of your building, plus the overhangs. You can measure that standing on the grass. The slope adds surface area, and the pitch multiplier accounts for it. That is the entire trick.

Climbing on a roof is dangerous and it is not necessary for an estimate. Falls from roofs are serious injuries. Shingles are slick, edges are unforgiving, and a ladder on soft ground moves. If your roof is steep, high, or cut up with hips and dormers, have a licensed roofer measure it. They do this daily and they carry insurance for it.

What you need

• A 25 ft or 100 ft tape measure.
• A helper to hold the other end.
• A notepad or your phone.
• Your roof pitch, which you can get from the ground or from the attic.

Step one: measure the length and width

Walk the outside of the house and measure the long side, then the short side. Measure at the ground but sight up to the edge of the roof, not the wall. The roof usually hangs past the wall, and that overhang is real shingled area you have to buy.

Round to the nearest foot. You are estimating, not machining a part. Write both numbers down.

Say you get 40 ft by 30 ft. That is your footprint: 40 x 30 = 1,200 sq ft. Hold onto that number, we will use it the whole way through.

Do you include overhangs?

Include them. The overhang, the eave that sticks out past the wall, gets shingled like everything else. If you measure wall to wall and ignore it, you will come up short on material.

The easy way: stand back, look up at the roof edge, and drop an imaginary plumb line to the ground. Measure to that spot, not to the siding. If you cannot eyeball it, measure the wall and add the overhang depth on each side. A 12 in overhang on both sides adds 2 ft to that dimension.

This is one of the most common places DIY estimates go wrong. Two feet on each dimension of a 40 x 30 house is not a rounding error.

How do you measure an L shaped roof?

Break it into rectangles. Almost every complex footprint is two or three simple rectangles stuck together. Measure each rectangle on its own, calculate its area, then add them together. Apply the pitch multiplier to the total at the end.

For an L shape, draw the outline on paper. Split it into a big rectangle and a smaller one so the two do not overlap. Measure the sides you can reach, and derive the rest from the sides you know. Then add the areas.

The Square Footage Calculator is handy here, it will add up your rectangles so you are not doing it on the back of an envelope.

Watch the overlaps

• Never count the same area twice where the rectangles meet.
• Include the overhangs on every outside edge, including the inside corner wings.
• Dormers, bay windows and porch roofs are their own small rectangles. Add them.
• Hips, valleys and dormers push waste toward 15%, so plan for it.

How do you find the roof pitch?

Pitch is rise over 12 in of run. A 6/12 roof rises 6 in for every 12 in it travels horizontally. You can measure it in the attic against a rafter with a level and a tape, or estimate it from the ground by sighting the gable end against a level held out at arm's length.

If you want the full method, see how to calculate roof pitch. For estimating purposes, being one step off (6/12 vs 7/12) changes your total by about 4%, which your waste allowance largely absorbs.

What are the roof pitch multipliers?

Each pitch has a fixed multiplier. Multiply your flat footprint by it to get the actual sloped surface area. Steeper roof, bigger multiplier, more shingles.

• 3/12 = 1.031
• 4/12 = 1.054
• 5/12 = 1.083
• 6/12 = 1.118
• 7/12 = 1.158
• 8/12 = 1.202
• 9/12 = 1.250
• 10/12 = 1.302
• 12/12 = 1.414

Notice how a 12/12 roof, a true 45 degree slope, needs about 41% more shingles than a flat footprint of the same size. Pitch matters more than most people expect.

The worked example, start to finish

Take that 40 x 30 ft building with a 6/12 roof.

Footprint

40 x 30 = 1,200 sq ft.

Apply the multiplier

6/12 pitch means a multiplier of 1.118.

1,200 x 1.118 = 1,342 sq ft of roof.

Convert to squares

One square is 100 sq ft. So divide by 100.

1,342 / 100 = 13.4 squares.

Convert to bundles

Standard three tab and architectural shingles run 3 bundles per square.

13.4 x 3 = 41 bundles.

Add waste

Add about 10% for a simple gable. That takes 41 bundles to 45 bundles. On a complex roof with hips, valleys and dormers, go to about 15% instead.

That is the full chain: footprint, multiplier, squares, bundles, waste. Run your own numbers through the Roofing Calculator and it will handle the multiplier and the squares for you. For more on bundle counts and coverage, see how many bundles of shingles do I need.

What about starter strip and ridge cap?

Those are ordered separately. They are not part of your field shingle count, and forgetting them is a second trip to the supplier.

Ridge cap is estimated from the linear feet of ridge and hip, not from area. So walk the roofline, measure the ridge along the top and every hip running down the corners, and add those lengths together. That total is what you are covering.

Starter strip runs along the eaves and usually the rakes. It is a linear measurement too. Measure the perimeter edges that need it.

When should you just get a roofer to measure?

Call a pro when the roof is steep, tall, or complicated. A cut up roof with multiple ridges, valleys, dormers and different pitches on different sections is genuinely hard to estimate from the ground, and the error compounds.

• Anything above one story, or a pitch steeper than about 8/12.
• Multiple roof planes at different pitches.
• You cannot see the full outline from any spot on the ground.
• You are getting quotes anyway, contractors measure for free as part of the bid.

Ground measuring is for budgeting and sanity checking a quote. It is not a substitute for a professional take off on a real job.

A note on scope

This is an estimating guide, not installation advice. Roofing is governed by local building code and usually requires a permit, and requirements for underlayment, ice and water shield, ventilation and fastening vary by jurisdiction. Check with your local building department before you order anything, and follow the shingle manufacturer's instructions for the product you buy.

Bottom line

Measure the footprint from the ground including overhangs, break odd shapes into rectangles, apply the pitch multiplier, divide by 100 for squares, multiply by 3 for bundles, then add 10% waste on a simple gable or 15% on a complex roof. Our 40 x 30 example at 6/12 came out to 1,342 sq ft, 13.4 squares, 41 bundles, 45 with waste. Order starter and ridge cap separately off linear feet. Stay off the roof, and if it is steep or complicated, let a licensed roofer measure it. Plug your numbers into the Roofing Calculator to get your area and squares in one step.