CalcHab

OSB & Plywood Sheathing Calculator

The OSB and plywood calculator determines panel requirements for subfloors, walls, partitions, and roof decking with cut waste allowances based on panel dimensions.

м
м
Total sheets (+ reserve)
8 sheets

Net sheets without waste: 7.4 sheets (+5% запас)

Total sheet coverage area:25 m²
Recommended thickness
15 - 18 мм

при кроці лаг 400 мм

Wood screws count (approx)
≈ 280 pcs

по 35 шт на лист

Пам'ятайте про термозазор 3 мм між сусідніми листами та 10-15 мм по периметру стін. OSB розширюється при зміні вологості!

Subfloor installation best practices

Expansion gaps: maintain a 3 mm gap between sheets and 10-15 mm around room perimeter walls.
Lay sheets in a staggered brick pattern with at least 40 cm joint offset; edges must align on joists.
Fastener spacing: 15 cm along perimeter edges and 30 cm along intermediate joists, 10 mm inset from edges.

How to use

  1. Select structural panel type: OSB-3 or structural plywood.
  2. Choose calculation input: room dimensions (length × width) or direct total surface area.
  3. Select panel format (2500 × 1250 mm or 1525 × 1525 mm).
  4. Choose application: subfloor over joists, wall sheathing, or roof deck.
  5. Specify cut waste allowance percentage (5% to 10%).
  6. Optionally enter unit cost per sheet.
  7. Review total sheets to order, purchased surface area, and required screws.

What Does the Sheet Sheathing Calculator Compute?

Panel count: total full boards required to cover designated areas.

Purchased square footage: total gross panel area including waste allowance.

Fastener count: recommended quantity of subfloor screws for perimeter and field fastening.

Sample Subfloor Calculation

Covering a 20 m² subfloor using 2500 × 1250 mm (3.125 m²) OSB panels requires 6.4 sheets net.

Ordering 7 sheets provides an adequate margin for staggered layout cutting.

Frequently Asked Questions

What is the surface area of a 2500×1250 mm sheet?

A standard panel covers exactly 3.125 square meters (33.6 sq ft).

What OSB thickness is required for 400 mm joists?

An 18 mm (approx. 3/4 inch) panel is standard for 400 mm joist spacing.

Why is an expansion gap required?

A 3 mm gap between sheets prevents buckling and floor squeaks from seasonal humidity changes.

Plywood versus OSB: which is better?

Plywood offers superior bending stiffness, while OSB-3 provides consistent density and moisture stability at lower cost.

How many screws are needed per panel?

Typically 35 to 45 subfloor screws spaced 150 mm along edges and 300 mm along intermediate supports.

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