What thickness underlayment?

2–3 mm under laminate; 1–1.5 mm under rigid core vinyl.

Do I need a vapor barrier?

Over concrete or on grade, yes, unless the pad has one built in.

Do you overlap underlayment?

No — butt seams and tape; overlap poly about 8 in.

What underlayment for laminate?

2–3 mm foam or denser pads for better acoustics.

Which blocks the most noise?

Cork, fiberboard or high-density foam.

Can I reuse old underlayment?

Not recommended — it loses thickness and performance.

Flooring underlayment calculator

Floor area, roll coverage and width, and whether you need a vapor barrier: you get underlayment rolls, seam tape and poly sheeting.

Purchase quantity

26.25 m²

Net measurement: 25 m² · Waste 5 %

Underlayment rolls2 roll
Seam tape25 m
Poly vapor barrier (8 in overlap)1 roll

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How it's calculated (visible formula)

rolls = ceil(area × (1 + waste) ÷ roll coverage); tape = area ÷ roll width; poly = area × 1.2

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Measure the floor area.
Choose underlayment for the flooring type.
Work out rolls with waste.
Work out seam tape.
Add a vapor barrier over concrete.

Worked example: 270 sq ft, 160 sq ft rolls (15 m²), over concrete

283 sq ft → 2 rolls
Tape ≈ 82 ft
Poly ≈ 323 sq ft → 1 roll

→ 2 underlayment rolls and 1 roll of poly.

Common mistakes

Overlapping underlayment (butt and tape it).
No vapor barrier over concrete.
Thick pad under rigid vinyl that forbids it.

Pro tips

Butt seams, don't overlap, and tape them.
Run poly 2 in up the wall and trim after baseboard.
Don't use thick pad under rigid vinyl unless allowed.
Over radiant heat, choose low-thermal-resistance pad.

From calculation to quote

Add labour, overhead and your margin, and generate the professional PDF.

Create quote Calculate margin & GST

FAQs

What thickness underlayment?: 2–3 mm under laminate; 1–1.5 mm under rigid core vinyl.
Do I need a vapor barrier?: Over concrete or on grade, yes, unless the pad has one built in.
Do you overlap underlayment?: No — butt seams and tape; overlap poly about 8 in.
What underlayment for laminate?: 2–3 mm foam or denser pads for better acoustics.
Which blocks the most noise?: Cork, fiberboard or high-density foam.
Can I reuse old underlayment?: Not recommended — it loses thickness and performance.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.