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Deck Stain Calculator

Created by Gabriela Diaz
Reviewed by Anna Szczepanek, PhD and Rijk de Wet
Last updated: Jan 18, 2024

The deck stain calculator will help you estimate the total area of your deck and the amount of stain that you need to cover it.

Maybe you're planning to install a deck, or about to start a renovation project, or you're simply daydreaming about your dreamed patio. You're probably wondering — "How do I calculate the amount of stain for the stairs and the railing?" or "Will 5 gallons of deck stain be enough?" Then this is the tool for you!

Keep reading to learn:

  • How to calculate the deck area yourself; and
  • How much stain do I need for my deck?

Haven't you yet installed a deck on your patio? Then, we recommend starting with our decking calculator for material and cost planning.

How to use the deck stain calculator?

Before you start using the deck stain calculator, first, you'll need to take some measurements 📏📐 Make sure you have your measuring tape at hand and go through the following checklist to verify that you have all the required values:

Begin by taking the floor's dimensions:

  • The total length of the floor; and
  • The total width of the floor.

Does your deck have a railing and do you want to include it in your project? if yes, then you'll also need:

  • The total length of the railing;
  • The height of the railing; and
  • The width of the posts. The calculator uses the minimum span of 72 inches between posts as suggested by building codes.

If you are including the balusters, then you'll require to know:

  • The number of balusters per foot or meter (The Balusters density field in the calculator); and
  • The balusters width.

Finally, if your deck area includes steps, you'll also need:

  • The total number of steps; and
  • Their width.

🙋 You can take these measurements in metric or imperial units (cm, m, in, or ft) — the calculator will do the conversions for you 😉

Now that you have all of your measures, you're ready to input them into the deck stain calculator's fields:

  1. Onto the Floor dimensions section, enter the values for length and width of the floor.

  2. Next, on the Railing dimensions, you'll find a drop-down menu where you can select whether you'd like to include (With railing) or not (No railing) into your calculations. Select Custom to input a custom area value for the railing.

  3. If you select the With railing option, you'll see the corresponding fields for entering the respective dimensions: Railing length, Railing height, and Posts width.

  4. On this same section, you'll see another drop-down menu (Filling), where you can choose to include or not the balusters of your railing into the area estimation.

  5. Finally, in the Steps dimensions section, you can choose to include or not the steps into the calculations with the Include steps drop-down menu.

  6. If you incorporate the steps, the calculator will display the fields to enter the dimensions corresponding to your deck stairs.

  7. Once you've inputted all this information, the calculator will show you the total deck area and the total amount of stain needed to cover your deck. If you want, you can change the number of coats that you'd like to apply. By default, it's set to one coat of deck stain.

Please note that these results are an approximation. Other factors, like the type of wood and the specific brand of stain that you use, can affect the amount of stain needed. By default, the calculator assumes that 1 gallon can cover up to 175 ft2. For other coverage factors, you can enter your custom value in the Coverage factor field.

🙋 On the Advanced mode of the deck stain calculator, you'll find the corresponding areas of each element of your deck.

How do I calculate the amount of stain needed for a deck?

To calculate the amount of stain that you need to cover your deck:

  1. Measure your floor's total Length and Width.
  2. Calculate the floor area as: Floor Area = Length × Width.
  3. Measure the railing's total Length and Height. With these, you can get an approximate value of the railing area: Railing Area = Length × Height.
  4. Estimate the deck's stairs' area with the total number of steps N, steps' width, run and rise: Steps Area = N × (Steps Width × (Run + Rise)).
  5. Calculate the total deck area: Total Area = Floor Area + Railing Area + Steps Area.
  6. Finally, divide the total area by the factor 175 ft2 per gallon to get the total amount of stain: Amount of stain = Total Area × (1 gal / 175 ft²).

Not sure about what the terms rise or run of a stair mean? Check out the stair calculator to learn about these and all the math behind a stair!

How much stain do I need for my deck with railing?

As mentioned above, step number three's formula will give you a rough estimate of the railing area. If you're interested in a more detailed calculation, below you'll find a step-by-step on how to calculate this area.

Railing with balusters and posts

Railing with no filling

If your railing doesn't have balusters and is filled with cables or glass, you'll only need the area of the railing's frame, which comprises the rails and the posts. Let's see how to estimate these values:

  • For the area of the posts:

    Posts Area = Number of Posts * 2 * Railing Height * (Railing Width + Railing Length)

  • To calculate the area of the rails:

    Rails Area = n * 2 * Rail Length * (Rail Width + Rail Height)

    Where n is 1 if there's only one rail, as shown in the image above, or 2 if you're considering the top and bottom rails.

  • Finally, the total railing's frame area is:

    Railing Frame Area = Posts Area + Rails Area

Railing with balusters

On the other hand, if your railing has balusters and you plan to include them in your project, you'll need to add the total area of these to the railing frame's area calculated before. The area will depend upon the geometry of your balusters:

  • For rectangular (or squared) section:

    Rectangular Baluster Area = Number of Balusters * Baluster Length* (Baluster Width + Baluster Height)

    The baluster's width and height are the same for a squared section.

  • For circular section:

    Cylindrical Baluster Area = Number of Balusters * π * Baluster Diameter * Baluster Length

Finally, simply add your baluster's area to the railing frame's area to calculate the total area:

Railing with Baluster Area = Railing Frame Area + Baluster Area

💡 The calculator assumes the balusters are of squared section. For the same width (diameter) and length, the area of cylindrical balusters is about 21.5% smaller.

At Omni, we have other tools that can help you plan and create your dreamed yard — give them a try:

  • If you're thinking about including a railing on your deck, you can use the baluster calculator to find out how many balusters you'll need 🔨
  • You can use the fence calculator to help you plan a fence-building project 🚧
  • With the paint calculator, you'll be able to determine how much paint you need to cover any wall in your home 🏠


How much stain do I need for my deck?

To stain your deck, you need approximately 1 gallon of stain to cover an area of 175 ft2. If you need to cover a smaller or bigger area, you can use this proportion as a reference and apply it to your required dimensions.

How much stain do I need for a 20x20 ft² deck?

To stain a 20x20 ft² deck area, you'll need approximately 2 and 1 quarter gallons (2.25 gal). You can get this result by assuming that 1 gallon can cover up to 175 ft2. Also, consider this amount is for one coat of stain. If you plan to apply more than one coat, multiply by the number of stain coats.

How much will a gallon of deck stain cover?

A gallon of stain can cover up to 175 ft2 approximately. This amount is for one coat of stain. Meaning that, if you're planning to apply more than one coat, you'll need to multiply by the number of coats.

How many square feet will 5 gallons of deck stain cover?

With 5 gallons of deck stain, you can cover around 875 ft2 of deck area. This result is an approximation — it depends on the type of wood and the number of coats you plan to apply.

Gabriela Diaz
Related calculators
Floor dimensions
Floor length
Floor width
Railing dimensions
Include railing
No railing
Steps dimensions
Include steps
No steps
Amount of stain
Number of coats
Coverage factor
/ US gal
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