Wood Stain Calculator

Wood Stain Calculator for decks, fences, siding and furniture. It adds up railings, steps and edges, applies each maker's spread rate to every coat, then lists which cans you need.

Planning a Stain Job With the Wood Stain Calculator

The Wood Stain Calculator works out how much stain a deck, fence, siding wall or set of cabinet doors needs, coat by coat. It uses the spread rate each maker prints for its own stain, then picks the cheapest mix of cans at the prices you enter.

Homeowners use it before a spring deck job, when running short halfway means a second trip to the store. Furniture makers and cabinet shops use the pieces mode, where faces, edges and a quart of pre-stain conditioner all have to be counted.

Measuring a Deck the Way Stain Makers Do

A deck is more than its floor. TWP, the deck stain maker, adds up a deck as the flooring plus the railings plus the steps, and it measures a fence as length times height, doubled when both sides get stain.

$$A=L\times W+L_r\times H_r+N_s\times W_s\times \frac{T+R}{12}$$

L and W are the deck's length and width, L_r and H_r are railing length and height, and N_s is the number of steps. W_s is step width in feet, while T and R are tread depth and riser height in inches, which is why they are divided by 12.

The default 16 by 12 ft deck has 192 sq ft of floor, 120 sq ft of railing at 40 ft long and 3 ft high, and 15 sq ft of treads on four steps. That adds up to 327 sq ft, and the railing alone is more than a third of it.

Siding is wall length times height minus windows and doors. For furniture and cabinets, enter each piece's real size in inches, pick which faces get stain, and add a thickness when the edges are stained too.

Stain Needed, Coat by Coat

Many exterior stains do not spread at the same rate on every coat. The first coat soaks into bare wood, and the second spreads much farther because the pores are already partly full.

$$V=\frac{A(1+w)}{R_1}+(n-1)\times \frac{A(1+w)}{R_2}$$

V is gallons, A is the stained area in square feet, w is the extra allowance as a decimal, and n is the number of coats. R_1 is the first-coat spread rate and R_2 the rate for later coats, both in sq ft per gallon.

Behr rates its Premium Semi-Transparent stain at 250 to 300 sq ft per gallon for the first coat and 500 to 600 for the second. On the 327 sq ft deck with 10 percent extra, the first coat takes 1.31 gallons and the second only 0.65, for 1.96 gallons in all.

That thin second coat is deliberate. Behr's data sheet lists 6.4 mils wet at 300 sq ft per gallon and 3.2 mils at 500, and warns that applying the stain too heavily leads to peeling and cracking.

Rough Wood Can Double the Order

The surface texture changes coverage more than most people expect. Cabot rates its Semi-Transparent Stain + Sealer from 200 to 650 sq ft per gallon, with 450 to 650 on smooth wood and 200 to 300 on rough-sawn boards.

On the same 327 sq ft deck with 10 percent extra, the smooth midpoint of 550 needs about 0.65 gallons. The rough midpoint of 250 needs about 1.44 gallons, so picking Rough or Weathered switches the calculator to the maker's rough-wood range.

Where a maker gives no separate rough figure, the tool uses the low end of its range for rough wood. The Maker's Low Rate and High Rate rows on the second result card show how far the order could swing either way.

One Coat or Two Depends on the Stain

Coat counts are not a matter of taste on exterior stains. Behr says two thin coats are required on its semi-transparent stain, while Cabot calls for one coat of its oil-based stain.

Setting Coats above the maker's count triggers a warning, because extra coats of a penetrating stain have nowhere to go. The stain stays on the surface, dries poorly and can turn glossy or tacky.

Pre-Stain Conditioner for Pine and Maple

Minwax describes its oil-based Pre-Stain Wood Conditioner as especially necessary on soft or porous woods such as pine, alder, birch and maple. These woods soak up stain unevenly and leave dark blotches without it.

Pick a Minwax stain and one of those species for furniture or a floor, and the calculator adds the conditioner to the plan. Twelve cabinet doors at 30 by 15 in, stained on both faces and edges, come to about 89 sq ft with 10 percent extra, so one quart rated at 125 sq ft covers the job.

Sanding also changes how stain takes, so work through the grits in the Sanding Schedule Calculator first. Interior stain still needs a clear topcoat, and the Varnish Coverage Calculator sizes that next step.

Limits, Units and the Cheapest Cans

The tool works in US units of feet, inches and gallons, and switches to meters, centimeters and liters in metric. The can sizes stay US, since half-pints, quarts, gallons and five-gallon pails are what US stores sell.

Deck sides run 1 to 500 ft, fence length up to 20,000 ft and piece counts up to 5,000. Windows and doors must be smaller than the wall they sit in, and any entry outside those limits pauses the results and highlights the field.

The can plan tries every mix of the sizes that stain is sold in. When one gallon costs less than the quarts needed to match it, the Wood Stain Calculator buys the gallon, even if a little more is left over.

Wood Stain Questions Before You Buy

How much area does a gallon of stain cover?

It depends on the product, the coat and the wood. Behr's semi-transparent stain covers 250 to 300 sq ft on the first coat and twice that on the second, while Cabot's oil stain ranges from 200 sq ft on rough wood to 650 on smooth.

Generic calculators often assume a single figure, such as 175 sq ft per gallon, for every stain. That can be off by half in either direction, so use the rate on your own can.

How much stain do I need for a 12 by 16 deck?

The floor alone is 192 sq ft, but railings and steps add much more than people expect. With 40 ft of railing 3 ft high and four steps, the total is 327 sq ft.

With two coats of Behr semi-transparent and 10 percent extra, that comes to about 1.96 gallons, so two gallons cover it. The same deck in one coat of Cabot on smooth wood needs well under one gallon.

How long should I wait before the second coat?

Makers set this on the label, and it differs a lot between products. Cabot lists 24 hours before recoating its oil-based semi-transparent stain, while Behr's water-based semi-transparent is ready for its second coat in 1 to 2 hours at 77 degrees F and 50 percent humidity.

The Finish Drying Time Calculator works out recoat and cure windows for common stains and finishes. Check the weather too, since Behr's current label asks for 40 to 90 degrees F and no rain in the forecast for 24 hours.