About this calculator
This calculator works out how much oil, stain or paint to buy for timber — a deck, a fence, cladding. Type the area, or let the calculator work it out from the boards: their number and size, one face or both, and optionally the edges and ends. The amount is the area divided by the product's spread rate, coat by coat; the first coat, on bare wood, has its own (usually lower) rate. Containers are rounded up, and you can let the calculator find the best mix of a large and a small can size.
Formula
board area = faces × L × W (+ 2 × L × T + 2 × W × T with edges and ends)
area = board area × number of boards (or typed)
first coat (l) = area / first-coat spread rate
further (l) = area × (coats − 1) / further-coat spread rate
with waste = (first + further) × (1 + waste %)
containers = ceil(with waste / container size)
mix = the counts of large and small containers that cover the need
with the least volume bought; on a tie, the fewest containers
Worked example
A deck of 30 boards 4000 × 140 × 28 mm, top face plus edges and ends, 2 coats at 8 m²/l (first) and 10 m²/l (second), 10 % waste, 2.7 l cans:
per board = 4000 × 140 + 2 × 4000 × 28 + 2 × 140 × 28 = 0.792 m²
area = 30 × 0.792 = 23.76 m²
first coat = 23.76 / 8 = 2.97 l
second = 23.76 / 10 = 2.38 l
total = 5.34 l; +10 % = 5.88 l → ceil(5.88 / 2.7) = 3 cans
For 15 m² the need is 3.71 l: two 2.7 l cans would buy 5.4 l, while one 2.7 l can and two 0.9 l cans buy 4.5 l — the calculator picks the latter.
FAQ
Where do the default spread rates come from? From Tikkurila's Valtti Color Extra data sheet: planed wood 8–12 m²/l, sawn wood 4–8 m²/l, two coats. The calculator uses 8 m²/l for the first coat and 10 m²/l for the next, because bare wood absorbs more; the data sheet itself gives one range for every coat. Pinotex Ultra Lasur states the same ranges. An oil spreads much further — Osmo's decking oil 24 m²/l per coat — so always enter your product's own figures.
Sawn or planed wood? Sawn (rough) wood takes considerably more: use the sawn-wood rate from your data sheet.
Should the edges and ends be finished? On decking, fences and cladding they usually are, and end grain soaks up the most. Untick the option if only the faces are treated.
Which standard applies? None. Spread rate is a product figure; the take-off is area divided by rate.
Assumptions and limits
No standard is cited: the quantity is area / spread rate.
Defaults to replace with your product's figures: spread rates 8 and 10 m²/l and the 2.7 l and 0.9 l cans (Tikkurila Valtti Color Extra), two coats, the 30-board example deck and the 10 % waste.
Geometry: boards are plain rectangles; grooves on ribbed decking, gaps, and the greater uptake of end grain are not modelled. All coats cover the same area.