How do I calculate planks for a floor?

Measure the room length and width in millimetres. Enter your plank dimensions (width and length). The calculator divides the room width by the plank width to get rows, and the room length by plank length to get planks per row. Always add 10% for waste from cuts and offcuts.

Should I include gaps between planks?

For outdoor decking, a 5–8mm gap is recommended for drainage and expansion. For interior flooring, tongue-and-groove planks typically have no visible gap. For cladding, the gap depends on the profile style.

How much waste should I allow for planking?

Allow 10% for standard rectangular rooms. For L-shaped rooms, rooms with many obstacles, or diagonal layouts, increase to 15%. For herringbone or chevron patterns, allow 15–20% waste.

What are standard plank widths?

Common UK plank widths are: flooring boards 90–140mm, decking boards 120–150mm, cladding boards 100–150mm, and wide-plank flooring 180–220mm. Length varies from 1800mm to 4800mm depending on the product.

WoodCalcs

Plank Calculator — Calculate Planks Needed

Work out how many planks you need to cover a given area, with waste allowance and cost estimate.

Area Length

Longest dimension of the area

Area Width

Shortest dimension of the area

Plank Width

Covering width of each plank

Plank Length

Length of each plank/board (longest dimension)

Gap Between Planks

0 for tongue and groove; 5-8mm for decking

Include 10% waste allowance

Adds the waste allowance to the plank count to cover end cuts and offcuts

Price per Plank (optional)

Enter your supplier price for a cost estimate

How We Calculate This

This calculator determines the number of planks needed to cover a rectangular area.

The calculation

Planks across = Area width ÷ (Plank width + Gap)

Planks along = Area length ÷ Plank length

Total planks = Planks across × Planks along

Each value is rounded up since partial planks require a full plank to cut from.

Waste allowance

The waste factor (default 10%, adjustable from 5% to 25% under Advanced options) covers end cuts, defective boards, and fitting around obstacles.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.