Underlayment Calculator

Calculate exactly how many rolls of roofing underlayment you need by type and roof size

Get a fast roll count from your roof area

Quick presets

sq ft

Estimated Materials

60 bundles

17.9 squares • 1,792 sq ft

PRO

Professional Calculator

Extended parameters for precise calculations

sq ft

Estimated Materials

60 bundles

Roof Area

1,792 sq ft

Squares

17.9

Detailed Breakdown

Roof Area1,792 sq ft
With Waste1,971 sq ft
Roofing Squares17.9
Bundles60
How to Use This Calculator
Using the Underlayment Calculator is simple and works for any roof size or underlayment type.

Quick Estimate tab: Enter your total roof area in square feet and select a waste factor. The calculator instantly shows how many rolls you need for each underlayment type, letting you compare at a glance. This is the fastest way to get a ballpark number for ordering.

Detailed tab: Choose your specific underlayment type (15 lb felt, 30 lb felt, synthetic, or ice & water shield) along with your roof area, pitch, and overlap preference. The calculator computes the exact number of rolls factoring in overlap waste and cut losses. Use this tab when you have already decided on your underlayment material and need a precise order quantity.

Budget tab: Enter your roof area, underlayment type, and state to get a full cost estimate including materials and installation labor. Labor costs are adjusted by state to reflect regional pricing differences. This tab helps you compare the true installed cost of different underlayment options.

The Formula
The underlayment calculation uses these formulas:

Effective Coverage per Roll = Nominal Coverage × (1 - Overlap%) For synthetic at 1,000 sq ft nominal with 10% overlap: 1,000 × 0.90 = 900 sq ft effective

Rolls Needed = (Roof Area × (1 + Waste%)) / Effective Coverage per Roll For a 1,700 sq ft roof with 10% waste and synthetic underlayment: (1,700 × 1.10) / 900 = 2.08 -> 3 rolls

Material Cost = Rolls × Cost per Roll 3 rolls × $130 = $390

Labor Cost = Roof Area / 100 × Labor Rate per Square 1,700 / 100 × $25 = $425
Example Calculation
Example: Average Home in Colorado

Tom has a 1,700 sq ft roof on his Denver home with a 5/12 pitch. He chooses synthetic underlayment for its durability in Colorado's weather.

Step 1: Determine effective coverage Synthetic roll nominal coverage: 1,000 sq ft With standard 4" overlap (~10%): 1,000 × 0.90 = 900 sq ft effective per roll

Step 2: Calculate rolls needed Roof area with 10% waste: 1,700 × 1.10 = 1,870 sq ft Rolls: 1,870 / 900 = 2.08 -> 3 rolls of synthetic underlayment

Step 3: Estimate cost
• Synthetic underlayment: 3 rolls × $130 = $390
• Cap nails / staples: ~$25
• Materials total: ~$415
• Labor (Colorado average): 17 squares × $25/sq = $425
• Total underlayment installed: ~$840

Frequently Asked Questions

How many rolls of underlayment do I need for a 1,700 sq ft roof?
It depends on the type. For synthetic underlayment (the most popular in 2026), you need about 2 rolls since each covers ~1,000 sq ft. For 15 lb felt, you need about 5 rolls (400 sq ft each). For 30 lb felt, you need about 9-10 rolls (200 sq ft each). Always add 10-15% for overlaps and waste.
What is the best type of roofing underlayment in 2026?
Synthetic underlayment is the industry standard for sloped roofs in 2026. It is lighter than felt, tear-resistant, slip-resistant for worker safety, and lasts up to 6 months exposed to UV. Brands like GAF FeltBuster, CertainTeed DiamondDeck, and Owens Corning ProArmor are top choices. Ice & water shield is required at eaves in cold climates and around penetrations.
Is 15 lb or 30 lb felt better for underlayment?
30 lb felt is significantly more durable and tear-resistant than 15 lb felt, making it the better choice if you are using felt. However, 15 lb felt is acceptable under asphalt shingles on standard-slope roofs. Most contractors in 2026 have switched to synthetic underlayment, which outperforms both felt options in durability, weight, and ease of installation.
Do I need underlayment under shingles?
Yes. Building codes require underlayment under asphalt shingles in virtually all US jurisdictions. Underlayment acts as a secondary weather barrier if wind-driven rain gets under the shingles, and it protects the roof deck during installation. Skipping underlayment voids most shingle warranties.
How much does roofing underlayment cost per roll in 2026?
In 2026, 15 lb felt costs $20-30 per roll (covers 400 sq ft). 30 lb felt costs $25-40 per roll (covers 200 sq ft). Synthetic underlayment costs $90-160 per roll (covers 1,000 sq ft). Ice & water shield costs $90-130 per roll (covers ~200 sq ft). Despite the higher per-roll price, synthetic often has the lowest cost per square foot.

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