Deck Stain Calculator

This deck stain calculator works out how many litres of decking stain or decking oil you need for a timber deck, and which tins to buy, for homeowners in the UK, Ireland and the rest of Europe. Enter the deck size, any steps or rails, the number of coats and the coverage printed on your tin, and the result updates as you type. It works in metres or feet.

Quick answer: multiply deck length by width, add steps and rails, multiply by the number of coats and divide by the coverage on the tin. The deck stain calculator does this for you: a 4.8 m by 3.6 m deck with 1.5 m² of steps needs about 4.7 litres for two coats at 8 m² per litre.

What Is a Deck Stain Calculator?

A deck stain calculator is a tool that turns the size of a deck into the litres of stain or oil needed to cover it with a chosen number of coats.

The formula is simple. Deck area equals length times width, plus any extra area for steps, risers and rails. Litres equal that area times the number of coats, divided by the coverage figure on your tin in square metres per litre. The tool then picks the mix of 5 litre, 2.5 litre and 1 litre tins that covers the job with the least paint left over.

The same maths works for decking oil, decking stain and decking paint, because every product states its coverage in the same unit. Only the coverage number changes. If you want to understand what stain actually does to timber, the Wikipedia article on wood stain gives a clear definition.

How Do You Use the Deck Stain Calculator?

1. Measure the deck length along the boards and enter it in metres, or switch to feet if you prefer.
2. Measure the deck width across the boards and enter it. Round up to the next 5 cm rather than down.
3. Add the extra area for steps, risers and rails in square metres. Leave it at 0 if the deck is flat with no extras.
4. Choose 1, 2 or 3 coats. Two coats is the usual choice for stain and oil on bare or weathered timber.
5. Type in the coverage printed on your tin, in m² per litre. The deck stain calculator starts at 8 as an example.
6. The deck stain calculator then shows the litres needed, the tin mix to buy and the litres per coat, then check the working shown under the result.

How Much Decking Stain Do I Need per Square Metre?

Plan on about 0.25 litres per square metre for two coats of a product that covers 8 m² per litre, which is 1 litre for every 4 m² of deck. That figure is only as good as the coverage you use, so always take the number from your own tin.

Coverage varies a lot between products. Ronseal states up to 8 m² per litre for its Ultimate Protection Decking Stain, with two coats and four hours between them. Its Quick Drying Decking Oil is listed at up to 9.5 m² per litre. Thinner oils tend to spread further than thick, coloured stains.

Note the words “up to”. Makers quote coverage on smooth, sound boards. Rough, grooved or weathered timber soaks up more, so real coverage is often lower. If you are unsure, enter a figure about 20% below the tin and let the deck stain calculator show you the safer total.

How Many Coats of Decking Stain Should You Apply?

Two coats is the standard for most decking stains and oils, and it is what manufacturers such as Ronseal specify for their decking products. One coat is usually only enough for a maintenance refresh on a deck that was treated recently and is still in good condition.

The first coat on new or very dry boards always takes the most product. That is why the deck stain calculator shows litres per coat as well as the total. If you are short on budget, buy enough for the first coat plus a margin, see how far it goes, then buy the second coat from the same batch number.

Three coats are sometimes suggested for very porous softwood or for a richer colour. Only add a third coat if the tin allows it, because some products can stay tacky or peel when overloaded.

How Do You Measure Steps, Rails and Odd Shaped Decks?

Measure each extra surface as a rectangle, add the areas together and enter the total in the extra area box of the deck stain calculator: one step tread 1.2 m long and 0.3 m deep is 0.36 m², and its riser adds a little more.

• Steps: count each tread and each riser. Tread length times depth, plus riser length times height, then multiply by the number of steps.
• Rails and balusters: estimate the rail length times its height for each face you will stain. Spindles take more time than stain, so a generous estimate is fine.
• L shaped decks: split the deck into two rectangles, add their areas and enter one combined length and width that gives the same total, or put the smaller part into the extra area box.
• Board edges and fascia boards: measure the visible face, often 15 cm deep, times the perimeter.

Treating the fence at the same time? Use our fence paint calculator for the panels, then add the two results together before you order.

Deck Stain Calculator Results by Deck Size

The table below was produced with the deck stain calculator at two coats and 8 m² per litre, with no steps or rails. Use it as a quick guide before you measure properly.

Does Grooved or Weathered Decking Need More Stain?

Yes: grooved, rough sawn and weathered boards all need noticeably more stain than smooth new boards of the same footprint, because they have more surface and absorb more on the first coat.

Grooves fold extra surface into each board, so the true area is larger than length times width. Some tins give a separate figure for grooved boards; if yours does, use it. If not, lower the coverage you enter in the deck stain calculator. The effect is large: an 18 m² deck needs 4.5 litres at 8 m² per litre but 9 litres at 4 m² per litre.

Grey, weathered timber should be cleaned and allowed to dry before staining, as the maker’s instructions require. A clean, dry board absorbs more evenly, which makes your estimate more reliable and the finish more even.

Worked Example: Gareth’s 4.8 m by 3.6 m Deck

Gareth in Leeds has a softwood deck measuring 4.8 m by 3.6 m, with three steps down to the lawn. He measures the treads and risers and gets 1.5 m² in total. His chosen stain says up to 8 m² per litre, two coats, so he enters those figures into the deck stain calculator.

• Deck area: 4.8 m x 3.6 m + 1.5 m² = 18.78 m²
• Stain: 18.8 x 2 coats / 8 m² per litre = 4.7 litres
• Litres per coat: 2.35
• Tins to buy: 1 x 5 L, leaving about 0.3 litres spare

The deck stain calculator suggests one 5 litre tin. Because the boards are a few years old and slightly grey, Gareth knows real coverage may fall below 8. He re-runs the numbers at 7 m² per litre, which gives about 5.4 litres, so he adds a 1 litre tin from the same batch to be safe.

What Are the Most Common Decking Stain Mistakes?

The most common mistake is measuring only the deck footprint and forgetting steps, risers and board edges, which can easily add 10% to the area of a small deck. A deck stain calculator only counts what you measure.

• Using the best case “up to” coverage on rough or grooved boards.
• Buying tins from different batches, which can show a colour change halfway across the deck.
• Staining in cold or damp weather. Ronseal advises a dry day above 10°C for its decking products.
• Applying the second coat too soon. Follow the recoat time on the tin.
• Ignoring the cost. Once you know the litres, our paint cost calculator totals tins, brushes and cleaner.

For more garden and indoor decorating tools, see the paint and decorating hub.

Deck Stain Calculator FAQs

Checked October 2026. Sources: Ronseal Ultimate Protection Decking Stain product page, Ronseal Quick Drying Decking Oil product page, Wikipedia: Wood stain.