Calculator
Roof size calculator
Get roof surface area and roofing squares from a measurement report, or estimate them from the house footprint and roof pitch. Every step of the math is shown.
Result
Enter your roof and press Calculate.
How this works
Roof area is the sloped surface, not the floor area. For one uniform pitch, the slope factor is √(1 + (rise ÷ 12)²). Multiply the horizontal footprint by that factor to get the surface area. A roofing square is 100 sq ft of roof surface. For a single pitch, gable and hip roofs over the same footprint have the same area, because every plane rises at the same rate.
This estimate misses dormers, extra valleys, mixed pitches and porch roofs. A measurement report is more accurate. Use the result to plan and to compare proposals, which should each state a measured area.
Next: turn the area into bundles or plan a replacement.
How to use this tool
- Pick how you know the roof: a measured area from a report, or the footprint (length × width, or plan area) plus the pitch.
- Find the pitch with the chart or a phone level app from inside the attic. Never climb onto the roof to measure.
- Add an overhang if you measured the house walls, not the roof edges.
- Read roof area and squares. Use them to check that every proposal is pricing the same size roof.
Measuring roofs in Ohio and Michigan
Many homes around Toledo, Detroit and the suburbs have attached garages, porch roofs and additions at a different pitch than the main roof. Enter each section separately so the total is right. In winter, measure from plans or an aerial report; never climb a snowy or icy roof.
Ways to get your roof area
| Method | Accuracy | Good for | Watch for |
|---|---|---|---|
| House size estimate | Rough | A first budget before anyone visits | Garages, porches and dormers are easy to miss |
| Footprint × pitch | Fair to good | Simple gable and hip roofs | Mixed pitches need one line per section |
| Aerial measurement report | Good | Complex roofs and comparing bids | Trees and shadows can hide edges |
| On-roof measurement by a contractor | Best | The final order and contract | Only a trained crew should be on the roof |
Get a free inspection or multiple bids
Free Asset Protection Inspection
Have the roof you're worried about looked at in person, at no cost and with no obligation. Homes, commercial buildings and HOA communities in Ohio and Michigan.
Inspections are done by our founder, Jonathan Blake, or, if you allow it, by the independent roofing and exterior contractor he works for.
Get three comparable bids
- Save or print this tool's result so every contractor starts from the same numbers.
- Ask at least three contractors for a written proposal on the same scope.
- Compare line by line: area, tear-off, repairs, materials, permits, warranty.
Why plan here first
| What you get | Midwest Roof Calculators | National cost websites | A first number on the doorstep |
|---|---|---|---|
| Built for Ohio and Michigan weather and permits | Yes | Rarely | Varies |
| Shows the formula and every assumption | Yes | Sometimes | Rarely |
| See results before giving contact details | Yes | Often not | No |
| Ranges labeled with what they include and exclude | Yes | Varies | Varies |
| Questions to ask every contractor | Yes | Sometimes | No |
| Replaces an in-person inspection | No, and we say so | No | No |
General comparison of approaches, not of any named company.
Frequently asked questions
Is roof area the same as my home’s square footage?
No. Living-space square footage counts floors, not the roof. A roof covers the footprint plus overhangs, and a sloped roof has more surface than the flat area under it. A 1,600 sq ft footprint with a 6/12 pitch has about 1,789 sq ft of roof once you include 1 ft overhangs.
What is a roofing square?
One roofing square is 100 square feet of roof surface. Roofers price and order by the square, so a 2,150 sq ft roof is 21.5 squares.
How do I find my roof pitch?
Pitch is the rise in inches for every 12 inches of horizontal run. You can measure it from the attic with a level and tape, read it from a phone level app on the gable end, or ask a roofer. See our roof pitch pages for the slope factor at each pitch.
Why does a hip roof come out the same as a gable roof?
When every roof plane has the same pitch, the surface area equals the footprint times the slope factor, whatever the shape. Hip roofs differ in ridge, hip and waste, not in total area.
How much waste should I allow?
It depends on the roof. Simple gable roofs need less, and roofs with valleys, hips and dormers need more. The calculator lets you choose because the right figure depends on your roof layout and the product.
Want your roof measured by a professional?
Ask for a professional measurement and inspection, or have this result emailed to you.