To estimate a roof replacement cost, find your roof’s size in squares, multiply by a typical price per square, then add the extras your roof is likely to need. A square is 100 square feet of roof. The sum takes about ten minutes, and it is close enough to tell you whether a bid makes sense.
The short version
- Measure the roof, not the house. The roof is bigger than the floor plan under it.
- Turn the footprint into roof area with a pitch number, then divide by 100 to get squares.
- Architectural asphalt shingles, the full system, typically run $6.00 to $9.00 per square foot installed.
- Then add what your roof may need: rotted decking, a second layer, skylights.
- Your estimate is a check on the bids. Only a measured roof gives you a real number.
Step 1: What is the footprint of your roof?
The footprint is the flat area the roof covers when you look straight down, eaves included. Walk around the house with a tape measure and split the outline into rectangles. An L-shaped house is two rectangles. A bump-out is one more.
Multiply length by width for each, then add them up. A one-story house with a footprint of about 1,800 square feet is our example from here on. Our guide to measuring a roof in squares covers the walk-around in more detail.
Step 2: How does the pitch change the roof’s size?
A steeper roof has more surface than the ground it sits over, so you multiply the footprint by a pitch number. This Old House says to multiply your roof’s square footage (opens in a new tab) by a number that adjusts for the extra shingles steepness needs, and its own example uses 1.118 for a 6:12 slope.
Pitch is how many inches the roof rises for every 12 inches it runs sideways. If you don’t know yours, finding the pitch from the attic is the safe way to do it. On our example, 1,800 square feet times 1.118 is about 2,012 square feet of roof.
Step 3: How many squares is that?
Divide the roof area by 100. Our example comes to about 20 squares. This is the number that matters, because roof area is often given in squares (opens in a new tab) and so is nearly every bid you will see.
Don’t pad this number. A waste allowance of 15% extra (opens in a new tab) is for someone ordering shingles to cover cuts. When you are pricing the job, a contractor already allows for it.
Step 4: What does a square cost around Ellicott City?
For architectural asphalt shingles, the full system typically runs $6.00 to $9.00 per square foot installed, depending on roof size, pitch, complexity and access. Our size table is a tighter guide than that per-foot range, because it already reflects how the price changes with size:
| Squares | Roof size | Typical full replacement |
|---|---|---|
| 15 | 1,500 sq ft | $10,500 to $13,500 |
| 20 | 2,000 sq ft | $13,500 to $17,500 |
| 25 | 2,500 sq ft | $16,500 to $21,500 |
| 30 | 3,000 sq ft | $19,500 to $25,500 |
| 35 | 3,500 sq ft | $22,500 to $29,500 |
Our 20 square example lands on the second row: $13,500 to $17,500. Run the per-foot range as a quick check and you get $12,000 to $18,000, which is wider and brackets it. The full list of sizes, from 1,000 to 8,000 square feet, is in our roof replacement cost guide.
One catch. Below about 10 squares, the cost of getting a crew and a dumpster to the house takes over, so a small job typically starts around $5,500 to $7,000.
What should you add on top?
Add the things that sit outside the standard price and that your roof is likely to have. These are the usual ones:
- Rotted decking. Sheathing boards that turn out to be bad cost $70 to $150 per 4x8 sheet installed. You can’t see them until the old shingles come off.
- A second layer. If two layers of old shingles are on there, the second tear-off adds a per-square charge.
- Skylights. Replacing one is quoted separately at $800 to $2,000+ each.
- Gutters, fascia and soffit. Taking gutters off and putting them back, or fixing rotted trim, is separate.
- Inside repairs. Drywall, paint and insulation are never part of the roof price.
It also helps to know which way your roof leans. A steep pitch (over 8/12), a cut-up roof shape, poor access and peak-season demand push a price up. A simple gable or hip roof, one story, good access and an off-season booking bring it down.
Step 5: How do you check an estimate against a bid?
Line the bid up with your numbers, one at a time. A good bid names the squares and the pitch, and you can check both against yours. Ask what it includes, using the list of what the full system covers. Ours covers tear-off of up to two layers, the dumpster and haul-away, synthetic underlayment, new drip edge, new flashing, vents, permits and the cleanup.
A low bid often just has a line missing. The most common one we see is reused flashing, which is cheaper on paper and is where roofs actually leak. This Old House suggests getting quotes from at least three roofing contractors (opens in a new tab), and we agree. Compare them on the same list, not on the bottom line.
Why is your estimate only a ballpark?
Because the parts that move the price most are the ones you can’t see from the ground: the decking, the number of layers, the exact pitch of each slope and the shape behind the trees. Tear-off gives the crew the chance (opens in a new tab) to inspect the roof deck, and that is when the surprises show up.
Our figures are also typical ranges for the area, not a price list or a quote. Use your estimate to decide whether a bid is sane, then get the roof measured.
Common questions
How much does it cost to replace a 2,000 square foot roof?
A 2,000 square foot roof, which is 20 squares, typically runs $13,500 to $17,500 for a full architectural asphalt system around Ellicott City. A 2,000 square foot house usually has more roof than that, because of the slope and the overhang.
Is it cheaper to estimate by square foot or by square?
They are the same math. A square is 100 square feet, so $6.00 to $9.00 per square foot is $600 to $900 per square. Roofers say squares because the numbers are smaller and every bid is written that way.
Do I need a pitch number to estimate the cost?
Yes, or at least a good guess. A steeper roof has more surface, which means more material, and a very steep one is slower and riskier to work on, which raises labor. Nobody has to climb up to find it: the attic gives you the same number.
Can I get an exact number without paying for it?
Yes. Our inspection is free, and the written report lists the measured square count and the pitch, separate from any proposal. There is no obligation to book anything.
What to do next
Once you have a ballpark, get the real measurements. Our free roof inspection gives you the squares, the pitch and the condition of the decking you can reach, with photos, so the number you hold is for your roof. If a new roof is the plan, our roof installation page shows what a replacement includes.
