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Calculate the underlayment rolls or sheets, seam tape, and vapor barrier needed for your flooring project. Supports foam, cork, rubber, and plywood underlayment types.
Floor underlayment is a thin material layer installed between the subfloor and the finished flooring surface. It serves multiple essential purposes including sound absorption, moisture protection, thermal insulation, and smoothing minor subfloor imperfections. The right underlayment can significantly extend the life of your flooring and improve comfort underfoot.
Our floor underlayment calculator helps you determine exactly how many rolls, sheets, seam tape, and vapor barrier materials you need based on your room dimensions, underlayment type, and subfloor conditions.
The most common and economical choice for laminate and vinyl flooring:
Premium natural material offering excellent acoustic and thermal properties:
Best-in-class sound dampening for multi-story buildings:
Rigid underlayment for creating a smooth, level surface:
Units Needed = (Floor Area × (1 + Overlap%)) ÷ Roll/Sheet Coverage
Where:
Floor Area = Length × Width (in square feet)
Overlap% = Typical 5-10% for seams and waste
For a 300 sq ft room using premium foam underlayment (200 sq ft per roll) with 5% overlap:
Adjusted Area = 300 × 1.05 = 315 sq ft
Rolls Needed = 315 ÷ 200 = 1.575 → 2 rolls
Tape Rolls = Floor Area ÷ 500
Example: 300 sq ft ÷ 500 = 0.6 → 1 roll of seam tape
Vapor Barrier Rolls = Adjusted Area ÷ 200
Only needed for concrete subfloors without built-in barrier
A vapor barrier (moisture barrier) prevents moisture from seeping up through the subfloor and damaging your flooring. Understanding when you need one is crucial for a successful installation.
Standard foam underlayment rolls cover 100-200 square feet each. For a 300 sq ft room with 5% overlap, you would need approximately 315 sq ft of underlayment, which equals 2 standard rolls (200 sq ft each) or 4 rolls if using 100 sq ft rolls.
Yes, underlayment is essential for laminate flooring. It provides cushioning, sound absorption, moisture protection (on concrete), and helps smooth minor subfloor imperfections. Some laminate comes with attached underlayment - check your product before purchasing additional underlayment.
No, vinyl plank (LVP) flooring requires specific underlayment. Use only underlayment approved for vinyl - typically thin foam (1.5-2mm) or cork. Never use thick foam underlayment as it can cause the vinyl planks to flex and damage the locking system. Check your flooring warranty requirements.
Thickness depends on your flooring type and needs. For laminate, 2-3mm foam works well. For hardwood, consider cork or rubber at 3-4mm for better sound control. Vinyl plank typically requires thinner 1.5-2mm underlayment. Thicker isn't always better - excess cushion can damage floating floors.
No, they serve different purposes. Vapor barrier blocks moisture migration from concrete subfloors, while underlayment provides cushioning and sound absorption. However, many premium underlayment products combine both functions with a built-in vapor barrier layer. On wood subfloors, you typically only need underlayment without vapor barrier.
You need vapor barrier if installing over concrete subfloors or any below-grade application (basement). Perform a moisture test: tape a 2×2' piece of plastic to the concrete for 24-48 hours. If moisture appears underneath, you definitely need vapor barrier. Most concrete installations benefit from vapor protection regardless of test results.
Generally no - double underlayment is not recommended. It creates too much cushion, which can damage floating floor locking systems and void your warranty. The exception is installing separate vapor barrier UNDER the underlayment on concrete, which is acceptable and often necessary.
Costs vary significantly by type: basic foam runs $15-25 per roll (200 sq ft), premium foam with vapor barrier $30-45 per roll, cork $50-80 per roll (100 sq ft), and rubber $60-100 per roll. For a 300 sq ft room, expect to spend $30-50 for basic foam, $75-100 for premium foam, or $150-250 for cork underlayment.
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