Underlayment Calculator — How Many Rolls Do You Need?
Underlayment is easy to underestimate — it is sold by roll size and you always need a little extra for overlaps and trimming. This calculator works out your floor area, adds a small waste allowance, and rounds up to the nearest whole roll.
How we calculate
Floor area = length × width. Area with waste = floor area × (1 + waste %). Rolls = ⌈area with waste ÷ roll coverage⌉.
Worked example
A 4 m × 3 m room (12 m²) with 5% waste needs 12.6 m². With 10 m² rolls: ⌈12.6 ÷ 10⌉ = 2 rolls.
Common mistakes
- Buying exactly enough rolls and running short when trimming around doorways and pipes.
- Overlapping underlayment sheets — this creates ridges under the finished floor.
- Using foam underlayment under vinyl planks with a built-in backing layer (creates too much give).
- Forgetting that some manufacturers void the warranty if the wrong underlayment type is used.
Frequently asked questions
How many rolls of underlayment do I need?+
Divide your floor area (plus 5% waste) by the roll coverage printed on the packaging. A 4 m × 3 m room needs about 12.6 m² — one 15 m² roll is enough, or two 10 m² rolls. Always round up to whole rolls.
What type of underlayment should I use under laminate?+
A 3–5 mm foam or combination foam/vapour-barrier underlayment is standard under laminate. If your laminate already has a pre-attached backing, check the manufacturer's instructions — some products require no additional underlayment.
Should I overlap underlayment sheets?+
No. Overlapping creates a ridge under the flooring that can cause movement and creak. Butt the sheets edge-to-edge and use tape only along the joint to hold them in place, not to overlap them.
Can I use the same underlayment under vinyl flooring?+
Only if the vinyl planks do not have a pre-attached foam backing. Most LVT and click vinyl planks already include backing — adding extra underlayment creates too much flex and can void the warranty. Always check the product specification.