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DIY Cost Tools

DIY Cost Tools

Carpet Underlay Roll Calculator

Plan carpet underlay area and whole rolls for a measured floor.

Number from 1 to 100000 sq ft.
Number from 0 to 100 %.
Number from 1 to 50 ft.
Number from 1 to 1000 ft.

Enter values in the units shown. Empty fields, fractions, comma-formatted numbers, values outside the listed ranges, and non-finite values are rejected.

Underlay area
Whole rolls

How to use this calculator

  1. Measure the project or enter costs from a current quote or product label.
  2. Adjust the quantities, coverage, package size, and allowances to match your situation.
  3. Select Calculate, then check the method, worked example, and limitations below.

Formula and method

Order area = floor area × (1 + waste%). Whole rolls = order area ÷ (roll width × roll length), rounded up.

Whole packages and pieces are rounded up. Results disappear when an input changes until the new values are calculated.

Worked example

Measured floor area 320 sq ft; Cutting waste 10 %; Roll width 6 ft; Roll length 30 ft. Results: Underlay area 352 sq ft; Whole rolls 2 rolls.

The example uses the values initially displayed in the fields.

Limitations

Complex room shapes and seam direction may require more rolls than the area-only estimate.

Review and reference

Reviewed October 5, 2026. The default example, input boundaries, arithmetic, rounding, and invalid input behavior were checked. The method is explained on How Our Calculators Work; replace example inputs with measurements or current product specifications. This is a planning estimate.

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