Quick answer
Rolls = area × (1 + waste) ÷ coverage per roll. 300 ft² with 10% waste is 330 ft², so 2 rolls of 200 ft².
Enter the area to cover, roll coverage and waste. The calculator returns rolls and area with waste. Use this ice and water shield calculator to check your own figures.
Related tools: Roof Pitch Calculator: Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor. Roof Shingles Calculator: Squares and bundles of shingles for a roof area. Metal Roofing Calculator: Number of metal roofing panels across a roof width.
How to use the Ice and Water Shield Calculator
- Enter area to cover (ft²) (above 0).
- Enter coverage per roll (ft²) (above 0).
- Enter waste allowance (%) (between 0 and 100). It starts at 10.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Area to cover | A number, in ft² | > 0 |
| Coverage per roll | A number, in ft². Printed on the roll | > 0 |
| Waste allowance | A number, in % | ≥ 0, ≤ 100, starts at 10 |
Formula and method
Formula
rolls = area × (1 + waste) ÷ coverage per roll
IEEE-754 double precision; shown to the decimals indicated.
Coverage per roll is on the packaging, so you enter it. Plan geometry only; confirm quantities with your supplier and local code before ordering.
Worked examples
This example is verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Area to cover = 300; Coverage per roll = 200; Waste allowance = 10.
| Result | Value |
|---|---|
| Rolls needed | 2 |
| Area with waste | 330 ft² |
The first line is the headline result (rolls needed). Below it the ice and Water Shield Calculator lists area with waste, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Where it goes
Ice and water membrane is applied along eaves (often to 2 ft inside the warm wall line), valleys, around penetrations and sometimes over the whole deck in cold climates. Add up each area before entering it.
Laps and rolls
Laps reduce the coverage of each roll, which the waste allowance covers. Round rolls up. Check the local code for how far up the roof it must extend.
How the result changes with area to cover
Holding every other input at the first worked example, this table changes only area to cover. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Area to cover | Rolls needed | Area with waste |
|---|---|---|
| 150 | 1 | 165 ft² |
| 300 | 2 | 330 ft² |
| 600 | 4 | 660 ft² |
| 1200 | 7 | 1,320 ft² |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Area to cover: entering "0" shows "Area to cover must be greater than 0." beside that field and no result.
- Coverage per roll: entering "0" shows "Coverage per roll must be greater than 0." beside that field and no result.
Choosing between the Ice and Water Shield Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Roof Pitch Calculator](/construction/roof-pitch-calculator/) | i know the and value | Pitch |
| [Roof Shingles Calculator](/construction/roof-shingles-calculator/) | roof area, bundles per square and waste allowance | Bundles needed |
| [Metal Roofing Calculator](/construction/metal-roofing-material-calculator/) | roof width to cover, panel coverage width and panel length | Panels needed |
| [Roof Sheathing Calculator](/construction/roof-sheathing-calculator/) | roof area, sheet size and waste allowance | Sheets needed |
| [Gutter Length Calculator](/construction/gutter-length-calculator/) | length of each eave and section length | Total gutter length |
Background: construction estimates
Material quantities are geometry plus a margin. Calculate the exact volume or area, add an allowance for waste, spillage, cuts and uneven ground (calculator pages commonly mention 5 to 10 percent, a rule of thumb that varies by material and job) and round up to whole units. One cubic yard is exactly 27 cubic feet.
Suppliers often have minimum order sizes and may charge for small loads, so confirm quantities, product yields and local code with your supplier or a qualified estimator before ordering.
Assumptions and limitations
- Round rolls up
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for area to cover and coverage per roll to confirm this.
Frequently asked questions
What is ice and water shield for?
It seals against water backing up under shingles.
How far up the roof?
Commonly to at least 24 inches inside the exterior wall.
Is it the same as felt?
No, it is a self-adhering membrane.
What does the Ice and Water Shield Calculator calculate?
Rolls of ice and water membrane for an area. It returns Rolls needed and Area with waste.
What formula does the Ice and Water Shield Calculator use?
rolls = area × (1 + waste) ÷ coverage per roll. Coverage per roll is on the packaging, so you enter it.
What do I need to enter in the ice and Water Shield Calculator?
You enter Area to cover (ft²), Coverage per roll (ft²) and Waste allowance (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Round rolls up.
What is an example of a ice and Water Shield result?
With area to cover 300, coverage per roll 200 and waste allowance 10, the rolls needed is 2.
Can I rely on this calculator for a decision?
Quantities are estimates. Add allowances for waste and site conditions, and follow local codes and a qualified professional's instructions for structural or safety-critical work. For this calculator in particular: Round rolls up.
Related calculators
- Roof Pitch Calculator — Roof pitch as rise per 12 inches, angle, slope percent and rafter length factor.
- Roof Shingles Calculator — Squares and bundles of shingles for a roof area.
- Metal Roofing Calculator — Number of metal roofing panels across a roof width.
- Roof Sheathing Calculator — Sheets of plywood or OSB for a roof area.
- Gutter Length Calculator — Total gutter length and number of sections from your eave lengths.
- Roof Area Calculator — Roof surface area from the building footprint, overhang and pitch.
Sources
- OpenStax, Prealgebra 2e (Rice University): perimeter, area, volume, circumference and the Pythagorean theorem
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international foot 0.3048 m, inch 25.4 mm, US gallon 3.785411784 L)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.