What thickness of subfloor?

23/32 in (¾ in) tongue-and-groove over joists at 16 in; 1⅛ in at 24 in.

Tongue-and-groove for floors: it shares loads between sheets.

How many screws per sheet?

Every 6 in on edges and 12 in in the field — about 50 per 4×8.

OSB or plywood subfloor?

OSB is cheaper; plywood handles moisture and edges better.

What screws for subfloor?

#8 or #10 subfloor screws, about 2 in long.

Can I lay hardwood directly on OSB?

Yes, with the right underlayment and fastening per the flooring maker.

Subfloor sheathing calculator

Floor area and sheet size: you get OSB or plywood sheets with waste, boxes of screws and tubes of construction adhesive.

Purchase quantity

11 sheet

Net measurement: 9.6 unit · Waste 10 %

OSB / plywood sheets11 sheet
Screws (about 1 per sq ft)2 box
Construction adhesive (1 tube per 100 sq ft)3 tube

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How it's calculated (visible formula)

sheets = ceil(area ÷ (length × width) × (1 + waste))

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.
Pick sheet size (4 × 8 ft is standard).
Divide area by sheet area and add 10% waste.
Work out screws and construction adhesive.
Plan the layout with staggered end joints.

Worked example: 320 sq ft with 4 × 8 ft sheets

32 sq ft per sheet
320 ÷ 32 = 10
+10% → 11 sheets

→ 11 sheets, 2 boxes of screws and 3 tubes of adhesive.

Common mistakes

Not staggering end joints.
Skipping the ⅛ in gap between sheets.
Using non-exposure-rated panels where they'll get wet.

Pro tips

Run the long edge perpendicular to the joists.
Glue to joists to stop squeaks.
Leave ⅛ in between sheets.
Use exposure-rated sheathing where it may get wet.

From calculation to quote

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

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FAQs

What thickness of subfloor?: 23/32 in (¾ in) tongue-and-groove over joists at 16 in; 1⅛ in at 24 in.
T&G or square edge?: Tongue-and-groove for floors: it shares loads between sheets.
How many screws per sheet?: Every 6 in on edges and 12 in in the field — about 50 per 4×8.
OSB or plywood subfloor?: OSB is cheaper; plywood handles moisture and edges better.
What screws for subfloor?: #8 or #10 subfloor screws, about 2 in long.
Can I lay hardwood directly on OSB?: Yes, with the right underlayment and fastening per the flooring maker.

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.