Offcut WorksDeck steps calculator
Enter the height from the ground to the top of the deck. You get the number of steps, equal riser heights, tread depth and stringers.
How the steps are worked out
Number of risers = total rise ÷ your target riser height, rounded to the nearest whole number. Riser height = total rise ÷ number of risers, so every riser is exactly the same.
The deck surface is the top step, so there is one fewer tread than risers. Total run = treads × tread depth. Stringer length = √(rise² + run²). Stringers = step width ÷ the largest spacing, rounded up, plus one.
Equal risers matter most
People rely on every step being the same height. One uneven riser is a common cause of trips, so the calculator adjusts the riser height after rounding so that all of them match. Aim for a target close to what you want and let the calculator work out the exact figure.
Which limits apply?
Two sets of figures are shown below the results, and they are different things:
- Comfortable garden steps. One community guide suggests risers of about 140 to 180 mm and treads of about 280 to 350 mm for outdoor steps. This is advice, not a rule.
- Approved Document K reference. For private stairs (stairs serving one dwelling), Approved Document K in England gives a rise of 150 to 220 mm, a going of 220 to 300 mm, a maximum pitch of 42 degrees, and twice the riser plus the going normally between 550 and 700 mm. The requirement applies only to steps that are part of the building, such as attached entrance steps. The document says it does not apply to steps on land leading to a building. Free-standing garden steps may therefore be outside it, but the figures are a sensible guide. If your deck is attached to the house, ask building control.
Other points from Approved Document K for dwellings
- Every rise and every going in a flight should be the same.
- Open risers are allowed in dwellings if treads overlap by at least 16 mm and a 100 mm sphere cannot pass through.
- Guarding is expected at the sides of flights and landings where the drop is more than 600 mm.
- Handrails go 900 to 1000 mm above the pitch line, on both sides if the stairs are 1000 mm or wider.
These apply where Approved Document K applies to your steps. Ask building control if you are not sure.
Materials
One decking supplier recommends stringers no more than 600 mm apart, and boards at least 28 mm thick on staircases because thinner boards flex. The calculator estimates tread board length from the tread depth, board width, gap and any overhang.
Before you build
- Measure the total rise from the finished ground level, including any paving or gravel you plan to add.
- Plan the landing at the bottom, because the bottom stringer needs firm support.
- Raised decks and steps may need handrails or guarding, so check the building regulations.
- Use non-slip surfaces and consider lighting for steps used in the dark.
Questions
How high should garden steps be?
One community guide suggests about 140 to 180 mm per riser for outdoor steps. Equal risers matter more than the exact height.
How do I work out the number of steps?
Divide the total rise by the riser height you want and round to the nearest whole number. Then divide the total rise by that number to get the exact riser.
Why is there one fewer tread than risers?
The deck surface acts as the top tread, so the last riser takes you up onto the deck.
Do garden steps need to meet building regulations?
Approved Document K applies to steps that are part of the building, such as attached entrance steps, and says it does not apply to steps on land leading to a building. Free-standing garden steps are usually outside it. If the deck is attached to the house, or you are not sure, ask your local building control.
Where the defaults come from
The Approved Document K figures were checked against the official document.
- Approved Document K: protection from falling, collision and impact (2013 edition, England, PDF). Table 1.1 for private stairs, the scope in paragraph 0.3, open risers in paragraph 1.9, handrails in paragraph 1.34 and guarding in paragraph 1.41. Read in full.
- Bunnings community: how to build garden steps. Comfortable outdoor riser and tread ranges. This is an Australian retailer's community advice.
- eDecks stringer data sheet (PDF). Stringers at no more than 600 mm centres and boards at least 28 mm thick on stairs.
- The comfortable garden step ranges (140 to 180 mm risers, 280 to 350 mm treads) come from an Australian retailer's community advice, not a UK standard.
- Whether Approved Document K applies to your steps depends on whether they are part of the building. We cannot tell that from here, so ask your building control team.