Quick answer: If your laminate flooring requires a separate underlayment, measure the surface it must cover, allow for trimming or seams according to the product instructions, and divide by the usable area printed on each roll. Round upward to whole rolls. First verify that your flooring system allows or requires the separate product.
Do you need separate underlayment?
Not all flooring systems use the same build-up. Some products include an attached pad, while others specify a compatible underlay and/or moisture-control layer. Avoid assuming that a second soft pad is always beneficial. Ask the flooring manufacturer which underlayment is approved for your exact product and subfloor. Pergo’s underlay guide, for example, discusses choosing underlay based on the installation location and whether the subfloor is wood or concrete.
Worked example: 14 × 12 ft room
Suppose the room is 14 × 12 ft, giving a gross area of 168 sq ft. Assume an 8 sq ft fixed feature will not receive this particular underlayment, leaving 160 sq ft. Whether to deduct a feature depends on the actual installation plan.
| Step | Calculation | Result |
|---|---|---|
| Gross room | 14 × 12 | 168 sq ft |
| Uncovered feature | 168 − 8 | 160 sq ft net |
| Illustrative trimming allowance | 160 × 1.05 | 168 sq ft to plan |
| Roll labeled 100 sq ft | 168 ÷ 100 = 1.68 | 2 full rolls |
The example requires two rolls at 100 sq ft per roll. Those rolls contain 200 sq ft of stated nominal coverage in total; this is not a guarantee of 200 usable installed square feet once cuts, layout and joint treatment are considered. The 5% allowance is a teaching example and not a mandatory manufacturer figure.
Seams, overlaps and actual usable coverage
Installation instructions may call for sheets to meet edge-to-edge, or for an integrated vapor film to overlap or have sealed seams. These are not interchangeable instructions. Do not subtract a presumed overlap length from every roll without checking the product. A roll advertised with coverage already accounting for its specific installation may need a different calculation than a roll whose label lists only gross dimensions.
Concrete, wood and moisture considerations
The subfloor influences the approved underlay and moisture-control approach. Pergo’s installation preparation guidance explains why a clean, flat subfloor is necessary before laying laminate. The same brand’s underlay range distinguishes products based on subfloor and intended performance. For a concrete slab, do not assume a generic foam layer provides the vapor protection required by your flooring system. For wood, avoid adding an unapproved moisture layer that could affect the assembly.
What your calculator can and cannot tell you
Our Underlayment Calculator takes measured area, excluded area, allowance and coverage per roll to calculate a number of rolls. It cannot certify moisture performance, compressive strength, acoustic rating or manufacturer warranty compatibility. Those decisions require the actual product instructions and job conditions.
Frequently asked questions
Should I buy underlayment for a floor with an attached pad?
Only if the flooring manufacturer’s instructions explicitly permit or require it. Two cushioning layers can be inappropriate for some locking floor systems.
Should I use the flooring box waste allowance for underlayment?
Not automatically. Plank cutting waste and underlayment roll cutting waste are different. Use an underlayment-specific estimate informed by its seam requirements.
Do I deduct cabinets or islands?
Deduct an area only if the approved installation will not cover it. Measure covered closets and doorways too.
Also see the laminate box planning guide to calculate flooring material separately. MaterialRaft estimates quantities only, not flooring suitability or waterproofing performance.