Ice and water shield calculator

Courses = round up((required width − overlap) ÷ (roll width − overlap)). Rolls = round up(courses × eave length ÷ roll length).

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Eave length (feet)

Required coverage width along roof (feet)

More inputs and assumptions

Roll coverage width (feet)

Roll length (feet)

Overlap between courses (feet)

Answer

…

Courses = round up((required width − overlap) ÷ (roll width − overlap)). Rolls = round up(courses × eave length ÷ roll length).

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

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Formula and assumptions

The required roof coverage width is your input; no local ice-barrier rule is inferred. Counts horizontal courses with overlap between them. End laps, valleys, cuts, damaged material and installation requirements are excluded. Confirm the required coverage and laps with the product instructions and applicable code.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-29

Using Ice and water shield calculator

Courses = round up((required width − overlap) ÷ (roll width − overlap)). Rolls = round up(courses × eave length ÷ roll length).

Next: Roofing calculator

Next: Roof pitch calculator

A worked example

For eave length (feet) = 60, required coverage width along roof (feet) = 6, roll coverage width (feet) = 3, roll length (feet) = 65, overlap between courses (feet) = 0.25, rolls = 3.

Before you use the result

Example results for eave length (feet)

These examples use Required coverage width along roof (feet): 6; Roll coverage width (feet): 3; Roll length (feet): 65; Overlap between courses (feet): 0.25. They are reference calculations, not recommended settings.

Eave length (feet)	Rolls
30	2
60	3
120	6

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ToolOctopus. “Ice and water shield calculator.” Updated 2026-09-29. https://tooloctopus.com/ice-water-shield-calculator.

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