How many squares is my roof, and what does that cost?
How many squares is my roof?
A roofing square is 100 square feet of roof surface. A pitched roof has more surface than the ground it covers, so the footprint, overhangs included, is multiplied by a pitch factor:
Roof area = (length + 2 × overhang) × (width + 2 × overhang) × √(1 + (pitch ÷ 12)²)
Squares = roof area ÷ 100
By our arithmetic, a 40 × 30 ft house with 12-inch overhangs and a 6/12 roof covers 42 × 32 = 1,344 sq ft, × 1.118 = 1,503 sq ft of roof: 15.0 squares, or 16.5 with a 10% waste allowance. When you enter square feet instead of length and width, the calculator treats the footprint as a square to add the overhang, so a long, narrow house comes out slightly low.
Roof pitch factors, 2/12 to 18/12
Roof pitch factors
| Pitch | Angle | Multiply the footprint by |
|---|---|---|
| 2/12 | 9.5° | 1.014 |
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 5/12 | 22.6° | 1.083 |
| 6/12 | 26.6° | 1.118 |
| 7/12 | 30.3° | 1.158 |
| 8/12 | 33.7° | 1.202 |
| 9/12 | 36.9° | 1.250 |
| 10/12 | 39.8° | 1.302 |
| 11/12 | 42.5° | 1.357 |
| 12/12 | 45.0° | 1.414 |
| 14/12 | 49.4° | 1.537 |
| 16/12 | 53.1° | 1.667 |
| 18/12 | 56.3° | 1.803 |
By our arithmetic: factor = √(1 + (pitch ÷ 12)²). The same factor applies to gable and hip roofs pitched the same on every side; dormers and mixed pitches add area the footprint method misses.
Michigan's residential code allows asphalt shingles only on slopes of 2/12 or steeper, and asks for double underlayment from 2/12 up to 4/12.
Roof replacement cost per square in Michigan
The calculator multiplies your roof's squares, before the waste allowance, by these published per-square prices, because the publisher defines a square as 100 sq ft of roof surface. Each publisher's figure is worked out on its own line; they are never blended into one range.
Published prices per square, by roofing type
Published prices per square
| Roofing | Published price | Who publishes it |
|---|---|---|
| 3-tab asphalt | $350 – $500 per square | Reasonable Contracting Services (Michigan cost guide) |
| Architectural asphalt | $450 – $750 per square | Reasonable Contracting Services (Michigan cost guide) |
| Premium or designer asphalt | $700 – $1,100 per square | Reasonable Contracting Services (Michigan cost guide) |
| Exposed-fastener metal | $650 – $1,000 per square | Reasonable Contracting Services (Michigan cost guide) |
| Standing-seam metal | $1,100 – $1,800 per square | Reasonable Contracting Services (Michigan cost guide) |
| Asphalt: where half of one roofer's published jobs landed | $6.00 – $7.07 per sq ft of roof | Roofing Army, Metro Detroit |
Installed prices as published, checked September 27, 2026. A square is 100 sq ft of roof surface. Reasonable Contracting's prices include tear-off of one layer, disposal, underlayment, the code-required ice barrier, flashing, ridge vent and labor.
For full-job prices in Royal Oak, and what adds to them, see the roof replacement cost guide.
What the range leaves out
- Rotten decking. Nobody knows how much needs replacing until the shingles are off; ask how it's priced per sheet.
- Steep, high roofs. Next Exteriors, a Mount Clemens roofer, says steep roofs, common on Tudors and colonials, can add 20 to 40 percent to labor.
- Extra layers. Reasonable Contracting's per-square prices include tearing off one layer; it publishes $30 – $60 per square ($1,000 – $2,000 on a typical home) for a second.
- The garage, chimneys, skylights and ventilation upgrades, which each add their own line to an estimate.
Tear-off or overlay?
Michigan's residential code doesn't allow new shingles over a roof that already has two or more layers, over slate or tile, or over a water-soaked or deteriorated roof; then everything comes off down to the deck. Where only one layer is on and it's sound, a re-cover may be allowed, but the decking can't be checked or replaced underneath it. The reroof permit and overlay checker takes you through the rules and the Royal Oak permit.
Common questions
How many squares is a 1,500 sq ft house?
It depends on the pitch and overhangs, not just the floor area. By our arithmetic, a 1,500 sq ft single-story footprint with no overhang at 6/12 has about 1,677 sq ft of roof, or 16.8 squares; at 10/12 it's about 1,953 sq ft, or 19.5 squares. A second story doesn't add roof; measure the footprint under the roof.
Does a hip roof have more area than a gable roof?
Not if every side has the same pitch: the roof area is the footprint (with overhangs) times the same pitch factor either way. Hip roofs do mean more cutting along the hips, so they usually need more waste allowance.
Where these figures come from
The prices and rules on this page come from these published pages, checked on October 5, 2026.
- Reasonable Contracting Services: roof replacement cost in Michigan · Michigan roof replacement cost guide, updated September 14, 2026: installed prices per square
- Roofing Army: roof replacement cost in Royal Oak · Metro Detroit roofer's cost guide from its own published jobs, September 2026
- Next Exteriors: roofing costs in Michigan · Mount Clemens roofer's cost-driver guide, March 2026
- Michigan Residential Code 2015, chapter 9: roof assemblies · State code text reproduced by Highland Township: ice barriers (R905.1.2), shingle slope (R905.2.2) and reroofing (R908)
- Michigan LARA: code books · State list of the construction codes in force; lists the 2015 Michigan Residential Code as the current code
