Most traditional roofing felt rolls cover about 216 to 432 square feet before overlaps. A common 15-pound roll is often listed at approximately 432 square feet, while a 30-pound roll may cover about 216 square feet. Actual coverage varies by product, and the amount of roof a roll covers is lower once laps and waste are included. The product label is the best source for its exact dimensions and stated coverage.
Meta description: Find out how many square feet are in a roll of tar paper, compare 15-pound and 30-pound roofing felt, and estimate rolls needed for a roof.
Typical Coverage in a Roll of Tar Paper
“Tar paper” is a common name for asphalt-saturated roofing felt, an underlayment installed between roof sheathing and shingles or other roofing materials. The name can be misleading: modern roofing felt is generally asphalt-saturated rather than coated with the kind of coal tar used in some other products.
Roll coverage depends on the felt’s weight designation, roll dimensions, and manufacturer. Traditional products are often sold in widths around 36 inches, but roll lengths differ. As a result, two products with the same weight designation may not have identical coverage.
| Common Product Description | Approximate Coverage Before Laps | Approximate Roofing Squares |
|---|---|---|
| 15-pound roofing felt | About 400–432 square feet | About 4.0–4.32 squares |
| 30-pound roofing felt | About 200–216 square feet | About 2.0–2.16 squares |
| Other felt or underlayment | Varies by product | Check the package |
These are common examples, not guaranteed specifications. Some packages list coverage in square feet; others provide roll dimensions or coverage in “squares.” A roofing square equals 100 square feet of roof area. It does not mean a 10-by-10-foot floor area unless the roof surface itself has that area.
Why Net Coverage Is Less Than the Roll’s Listed Area
Listed coverage generally describes the material’s area when laid flat, or a manufacturer’s stated coverage under specified installation conditions. On a roof, neighboring courses overlap, and the ends of rolls may overlap too. Those laps use material without adding the same amount of covered roof area.
For example, a 36-inch-wide roll installed with a 2-inch side lap covers about 34 inches of roof width per course. That is roughly 94% of the roll’s width before accounting for end laps, trimming, roof features, or damage. The actual result depends on the product instructions and installation layout.
End laps, valleys, ridges, hips, dormers, chimneys, and roof penetrations can increase material use. Roofs with many angles or interruptions often need more underlayment than a simple rectangular roof with the same measured area. Cutting and handling also create some waste.
For a rough planning estimate, a homeowner might allow several percent beyond the roof’s measured area for laps and waste. That allowance is not a substitute for the manufacturer’s instructions or a contractor’s takeoff. Steeper, complex, or unusually shaped roofs may need a larger allowance.
How to Calculate How Many Rolls Are Needed
A useful estimate requires three figures: the roof’s surface area, the product’s stated coverage, and an allowance for laps and waste. Measuring only the home’s footprint usually understates the roof area because it does not account for the roof’s slope or overhangs.
- Find the roof surface area. Use roof plans, measurements, or a reliable roofing estimate. If only the horizontal footprint is known, adjust for roof pitch and include overhangs.
- Check the roll label. Use the coverage printed on the exact product rather than assuming every roll of 15-pound or 30-pound felt is the same.
- Allow for overlaps and cutting. Follow the product’s required lap dimensions and account for roof complexity.
- Divide and round up. Divide the adjusted roof area by the product’s effective coverage per roll. Always round up to whole rolls.
Basic formula: Rolls needed = roof area, including an allowance for laps and waste, divided by the roll’s stated coverage. The result is rounded up to the next whole roll.
Example Estimate
Suppose a roof has 1,800 square feet of measured surface area and the project estimate includes a 10% allowance for laps and waste. The adjusted area is 1,980 square feet. If the selected felt roll is labeled for 432 square feet, the calculation is 1,980 ÷ 432, or about 4.58 rolls. The buyer would need five rolls.
This example is for estimating only. If the manufacturer states a lower coverage figure for the required installation method, that figure should be used instead. The appropriate waste allowance also varies with the roof and how the material is installed.
How Roof Pitch Affects the Estimate
Roof pitch describes how much a roof rises vertically over a horizontal distance. A sloped roof has more surface area than its horizontal footprint. The steeper the roof, the greater the difference, although the exact adjustment depends on the pitch.
For a simple roof plane, the surface-area multiplier can be calculated using the rise and run. For example, a 6:12 roof rises 6 inches for every 12 inches of horizontal run. Its area is greater than the corresponding flat footprint, so using the footprint alone will result in too few rolls.
Roof area calculators and roofing estimates often apply a pitch factor. When using one, the estimate should also account for all roof planes, overhangs, valleys, and other details. If the pitch or layout is uncertain, a roofing professional can measure the surface and prepare a material takeoff.
15-Pound vs. 30-Pound Roofing Felt
The “pound” labels are traditional product descriptions, not a direct way to calculate coverage. In many common product lines, 15-pound felt covers roughly twice as much area per roll as 30-pound felt because the rolls differ in length or amount of material. The label alone does not establish exact dimensions, weight, performance, or code compliance.
Heavier felt is not automatically the right choice for every roof. Selection depends on the roofing material, roof design, local requirements, climate, and product instructions. Some shingle systems allow specific types of asphalt felt; others may call for a different underlayment or installation method. The chosen underlayment must be compatible with the roof covering.
Modern alternatives include synthetic underlayments and self-adhered products. Their roll sizes and coverage can differ substantially from traditional felt, so “how many square feet in a roll of tar paper” is not a reliable way to estimate those materials. Compare the package’s stated coverage and required overlap instead.
What to Check on the Product Label
Before buying, confirm the roll’s actual coverage and the conditions under which that coverage applies. Product labels and installation instructions may specify required side laps, end laps, fastening, exposure limits, and acceptable roof coverings. These details affect both material calculations and proper installation.
- Product type: Confirm whether it is asphalt-saturated felt, synthetic underlayment, or a self-adhered membrane.
- Roll dimensions: Check the width and length if coverage is not clearly stated.
- Coverage: Look for square feet per roll or the number of roofing squares covered.
- Overlap requirements: Use the specified laps rather than assuming a standard measurement.
- Installation limits: Check permitted roof slope, exposure, fastening, and weather conditions.
- Code and system compatibility: Confirm local building requirements and the roofing manufacturer’s instructions.
Common Estimating Mistakes
Assuming Every Roll Covers the Same Area
Roll dimensions vary, even among products with similar labels. A familiar rule of thumb can help with an early estimate, but it should not determine the final purchase. Product-specific coverage is more dependable.
Using the House’s Footprint as the Roof Area
The footprint does not include the roof’s slope or overhangs. A pitch-adjusted roof measurement is needed for a more accurate estimate.
Ignoring Overlaps and Roof Details
Material used for laps and cuts reduces effective coverage. Complex roof geometry usually increases waste compared with a broad, uninterrupted roof plane.
Confusing a Roofing Square With a Roll
A square is a unit of roof area equal to 100 square feet. It is not a standard roll size. One roll may cover multiple squares, depending on the product.
Where to Find Reliable Product Information
The product package and manufacturer’s installation instructions should guide coverage and installation decisions. Roofing manufacturers such as GAF publish product information and installation resources for their underlayments; local building departments can provide information about applicable requirements. For a larger or complicated roof, a qualified roofing contractor can verify measurements and estimate the material needed.
Useful starting points include GAF technical information and the International Code Council. Requirements can vary by location and by roof assembly, so general guidance should not replace the applicable code, product instructions, or professional advice.
Quick Answer
A common 15-pound tar paper roll covers about 400 to 432 square feet before overlaps, while a common 30-pound roll covers about 200 to 216 square feet. The actual figure depends on the product, and usable roof coverage is lower when laps and waste are included. Check the roll label, measure the roof surface rather than the home’s footprint, and round the final roll estimate up.