Deck Stair Calculator

Risers = total rise ÷ the tallest step allowed, rounded up: 42 inches of rise at no more than 7.75 in a step takes 6 equal risers of 7 inches and 5 treads, a 50-inch run.

Your measurements

Example

Use the unit shown for each box, or type another one: 12 ft 6 in, 150 in, 3.8 m and 600 mm all work, as do the marks on a tape measure.

Finished deck to landing Chosen maximum riser Chosen tread run

Example: replace these measurements

Your stair layout

6 equal risers

Your measured layout

Side view, including the rise to the deck. This is stair geometry, not a stringer cutting or attachment plan.

Your measured layout

6 equal risers

Quantities and package details

Height of each riser: 7 in
Separate treads: 5
Total horizontal run: 50 in
First-to-last marking slope: 61.0328 in

The sloping measurement is not a finished stringer cut length. Confirm local requirements and attachment details.

The calculation

ceil(42 ÷ 7.75) = 6 risers
42 ÷ 6 = 7 in per riser
5 × 10 = 50 in horizontal run

Common questions

How many steps do I need for my deck?

Divide the total rise by the tallest riser you allow and round up. A 42-inch rise with a 7 3/4-inch maximum riser takes 6 risers of 7 inches each.

What is the maximum riser height for deck stairs?

The American Wood Council’s DCA 6 guide, based on the 2015 IRC, shows a 7 3/4-inch maximum riser and a 10-inch minimum tread. Your local code sets the rule where you live.

How long is the stringer?

The calculator gives the total run and the first-to-last marking slope, not a cut stringer length; the top attachment and bottom cut change it.

How to plan the quantity

Measure total rise between the finished deck and finished landing. Dividing by the chosen maximum and rounding up gives the number of equal risers.

The deck acts as the top tread, so the number of separate treads is one less than the riser count. Total horizontal run is tread count times tread run.

The sloping reference length connects the first and last step marks. It is not a stringer cut length: the upper attachment, bottom cut, nosing and actual board geometry still need a detailed plan.

Before you order

The editable starting limits reflect the cited AWC guide, not a statement of the code at your address. Confirm riser, tread, headroom, landing, handrail and guard requirements locally.
This does not size or approve a cut stringer. Keep finished tread thickness and the bottom/top connections in the drawing.

Before ordering, read the guide: How many deck boards do I need? Boards, gaps and screws. Or choose another calculator.