Measure the building footprint on the ground to the outside of the eaves, then multiply by the pitch multiplier. A 2,000 square foot footprint at a 6/12 pitch is 2,236 square feet of roof — 22.36 roofing squares. Divide the roof area by 100 to get squares, then add 10% to 20% waste.
Use the Roof Area Calculator to quickly determine your total roof surface area in square feet and in roofing squares (1 square = 100 sq ft). Just enter the building footprint length and width and your roof pitch, and the tool applies the correct slope multiplier to convert flat footprint area into actual sloped roof area. Accurate roof area is the foundation of every roofing estimate — shingles, underlayment, plywood, drip edge, ridge cap, and labor are all priced per square. Use the result here as the starting point for the rest of our calculators.
Roof square footage is the building footprint multiplied by the pitch factor. Measuring the outline on the ground and applying the multiplier is far quicker and safer than trying to measure the slope itself, and it gives exactly the same answer.
| Step | What you measure | What it gives you |
|---|---|---|
| 1 | Footprint length x width, to the outside of the eaves and rakes | Ground area the roof covers |
| 2 | Rise over a level 12 inches, taken off a rafter in the attic | The pitch, and its multiplier |
| 3 | Footprint x multiplier | Actual roof square footage |
| 4 | Roof square footage ÷ 100 | Roofing squares — the unit everything is priced in |
| 5 | Squares + 10% to 20% | Squares to order material against |
A 2,000 square foot footprint at a 6/12 pitch is 2,236 square feet of roof, which is 22.36 squares, or 24.6 squares once 10% waste is added.
| Footprint | 3/12 | 4/12 | 6/12 | 8/12 | 10/12 | 12/12 |
|---|---|---|---|---|---|---|
| 1,000 sq ft | 1,031 sq ft | 1,054 sq ft | 1,118 sq ft | 1,202 sq ft | 1,302 sq ft | 1,414 sq ft |
| 1,500 sq ft | 1,546 sq ft | 1,581 sq ft | 1,677 sq ft | 1,803 sq ft | 1,953 sq ft | 2,121 sq ft |
| 2,000 sq ft | 2,062 sq ft | 2,108 sq ft | 2,236 sq ft | 2,404 sq ft | 2,603 sq ft | 2,828 sq ft |
| 2,500 sq ft | 2,577 sq ft | 2,635 sq ft | 2,795 sq ft | 3,005 sq ft | 3,254 sq ft | 3,536 sq ft |
| 3,000 sq ft | 3,092 sq ft | 3,162 sq ft | 3,354 sq ft | 3,606 sq ft | 3,905 sq ft | 4,243 sq ft |
The difference between a 3/12 and a 12/12 roof on the same footprint is about 34% more material — several thousand dollars on a full reroof, and the single most common reason an order comes up short.
| Footprint | 4/12 | 6/12 | 8/12 | 12/12 |
|---|---|---|---|---|
| 1,000 sq ft | 10.5 | 11.2 | 12 | 14.1 |
| 1,500 sq ft | 15.8 | 16.8 | 18 | 21.2 |
| 2,000 sq ft | 21.1 | 22.4 | 24 | 28.3 |
| 2,500 sq ft | 26.4 | 28 | 30 | 35.4 |
| 3,000 sq ft | 31.6 | 33.5 | 36.1 | 42.4 |
One roofing square is 100 square feet of finished roof surface. It is the unit material is priced and ordered in, and three bundles of standard architectural shingle cover one.
| Square feet of roof | Roofing squares | Shingle bundles at 3/square |
|---|---|---|
| 500 sq ft | 5 | 15 |
| 1,000 sq ft | 10 | 30 |
| 1,500 sq ft | 15 | 45 |
| 2,000 sq ft | 20 | 60 |
| 2,500 sq ft | 25 | 75 |
| 3,000 sq ft | 30 | 90 |
| 4,000 sq ft | 40 | 120 |
To go the other way, multiply squares by 100. Twenty-five squares is 2,500 square feet of roof.
Not from this site — it does not look up addresses, and it does not ask for one. What a satellite measurement gives you is the footprint, which is only half the answer: the pitch multiplier still has to be applied on top of it, and a satellite image cannot see the pitch.
If you want to use one, measure the roof outline in a mapping tool to get the footprint, then take the pitch yourself from a rafter in the attic and multiply. That combination is as accurate as anything a paid report will give you, and it costs nothing.
A satellite reading also cannot see the valleys, the wall runs or the penetrations, and those are what buy the flashing. Any estimate that stops at the area is short of the parts that keep water out.
Roof area is the input to almost every material on the roof, but only the field material comes off it.
| From the area | From a perimeter measurement instead |
|---|---|
| Shingles — 3 bundles per square | Ridge cap — along every ridge and hip |
| Sheathing — 3.125 sheets of 4x8 per square | Drip edge — along every eave and rake |
| Underlayment — by roll coverage | Starter strip — eaves and rakes both |
| Nails — about 264 per square, architectural | Valley metal — measured along the valley line |
| Coating — by the pail coverage rate | Step flashing — one piece per shingle course |
That second column is why an estimate worked from the area alone always comes up short, and it is the most common reason a job stops for a second delivery.
The figure people usually have is the floor area of the house, not the roof, and the two differ by the pitch. These work both readings side by side.
100 sq ft · 200 sq ft · 400 sq ft · 1,000 sq ft · 1,200 sq ft · 1,500 sq ft · 1,800 sq ft · 2,000 sq ft · 2,400 sq ft · 2,500 sq ft · 3,000 sq ft
These come up constantly when ordering, and the answer is different for every material — some figures are fixed by definition and some are printed on the wrapper and vary by brand.
How many sheets of plywood are in a bundle? · How many sheets of OSB are in a bundle? · How many linear feet does a bundle of ridge cap cover? · Every coverage figure in one table
Measure the building footprint to the outside of the eaves, then multiply by the pitch multiplier. A 2,000 square foot footprint at 6/12 pitch is 2,236 square feet of roof. Divide by 100 for roofing squares, then add 10% to 20% waste.
Exactly 100 square feet of finished roof surface. A 2,236 square foot roof is 22.36 squares. Three bundles of standard architectural shingles cover one square.
The footprint, on the ground, then apply the pitch multiplier. It is faster, far safer, and gives the same answer as measuring up the slope — which is why nobody who does this for a living measures the slope.
A satellite measurement gives you the footprint, but not the pitch — and without the pitch multiplier the footprint understates the roof by 5% to 41%. Measure the outline in a mapping tool if you like, then take the pitch off a rafter and multiply.
Yes. The overhang is roof you have to cover, so measure to the outside edge of the eaves and rakes. A 16-inch overhang all round adds well over a hundred square feet on a typical house.