Deck Stringer Calculator: Rise, Run & Cuts

A deck stringer calculator works out the rise, run, and number of steps for a set of stair stringers, so you can cut the notches correctly before assembly. You enter the total rise (deck height to ground), the total run (horizontal distance), and the desired tread depth, and it returns the individual step rise, step run, and the number of treads needed. This page explains the formula, shows a worked example, and covers the common mistakes that lead to uneven or unsafe stairs.

Formula

The core formula for stair stringers is simple division, but the trick is choosing the right number of steps. The standard building rule is that each step rise should be between 4 and 7.75 inches (10.2 to 19.7 cm), with 7.5 inches being a comfortable target for most decks. The number of steps is found by dividing the total rise by the desired step rise and rounding to the nearest whole number:

Number of steps = round(Total rise ÷ 7.5)

Once you have the number of steps, the actual step rise and step run are:

Step rise = Total rise ÷ Number of steps

Step run = Total run ÷ Number of steps

Where:

• Total rise – vertical distance from the ground to the top of the deck, in inches (or cm).
• Total run – horizontal distance the stairs cover, in inches (or cm).
• Tread depth – the horizontal depth of each step, typically 10–11 inches (25–28 cm).
• Step rise – the vertical height of each step, in inches.
• Step run – the horizontal depth of each step, in inches.

Note that the calculator uses the total run you input, not the tread depth, to compute the step run. If you want a specific tread depth, set the total run to (tread depth × number of steps).

Worked Example

Using the default values from the calculator above:

• Total rise = 30 inches
• Total run = 36 inches
• Tread depth = 10 inches

First, find the number of steps: 30 ÷ 7.5 = 4, so we have 4 steps.

Step rise = 30 ÷ 4 = 7.5 inches.

Step run = 36 ÷ 4 = 9 inches.

The calculator shows: step rise = 7.50 in, step run = 9.00 in, number of steps = 4. That matches the formula exactly.

How to Use the Results

The step rise and step run tell you where to cut the notches on a 2×12 stringer board. Each notch is a right triangle with a vertical leg equal to the step rise and a horizontal leg equal to the step run. The top of the stringer is cut to rest against the deck rim, and the bottom is cut to sit on the ground or a concrete pad.

When you mark the stringer, start at the top and measure down one step rise for the first notch, then continue down for each subsequent step. The actual tread depth you use should be at least the step run, but most codes require a minimum of 10 inches. If your step run is less than 10 inches, you may need to extend the tread beyond the stringer or adjust the total run.

Common Mistakes and Misconceptions

One frequent error is confusing total rise with the height of the deck floor. The total rise is measured from the finished ground surface to the top of the decking, not to the top of the joists. If you measure to the joist, your steps will be too short by the thickness of the decking.

Another mistake is using the tread depth as the horizontal run for each step. The tread depth is the actual surface you step on, but the stringer notch is cut to the step run, which is the horizontal distance between consecutive step noses. If you cut the notch to the tread depth, the steps will be too deep and the stairs will extend farther than planned.

A third issue is ignoring the thickness of the tread material. If you plan to add a 1-inch thick tread on top of the stringer, the actual step rise will be reduced by 1 inch. Many builders subtract the tread thickness from the step rise when cutting the stringer to keep the final rise within code.

Choosing the Right Total Run

The total run is often dictated by the space available at the bottom of the stairs. A common rule of thumb is that the total run should be about 1.5 times the total rise for comfortable stairs. For example, a 30-inch rise would have a total run of 45 inches, giving a step run of 11.25 inches with 4 steps. This is close to the ideal 11-inch tread depth.

If you have limited space, you can increase the step rise (up to 7.75 inches max) and reduce the step run, but this makes the stairs steeper and less comfortable. Conversely, if you have plenty of space, a longer run with a shallower rise is easier to climb.

Safety and Code Considerations

Building codes vary by location, but most follow the International Residential Code (IRC) for residential stairs. The IRC specifies a maximum rise of 7.75 inches and a minimum run of 10 inches. It also requires that all steps have the same rise and run within a tolerance of 3/8 inch. Uneven steps are a leading cause of trips and falls.

Always check your local code before cutting. The calculator gives you a starting point, but it does not account for local amendments or special conditions like winders or landings. If your total rise is more than 8 feet, you may need a landing in the middle.

Alternatives and Adjustments

If the calculated step rise is too high or too low, you can adjust the number of steps. For example, a 30-inch rise with 3 steps gives a 10-inch rise, which is too steep. With 5 steps, the rise is 6 inches, which is comfortable but requires a longer total run. The calculator rounds to the nearest step, but you can manually override the number of steps by changing the total run to force a different count.

For curved or angled stairs, a simple stringer calculator is not sufficient. You would need to use a framing square or specialized software to lay out the stringer. Similarly, if you are building a deck with a landing, you need to calculate the stringer for each flight separately.

Frequently Asked Questions

How do I measure the total rise for a deck?

Measure from the finished ground surface (where the bottom of the stringer will rest) to the top of the decking surface. Use a level and a straight board to transfer the height if the ground is uneven. Do not include the thickness of the decking in the rise.

What is the ideal step rise and run?

For most decks, a step rise of 7 to 7.5 inches and a step run of 10 to 11 inches feels comfortable. The IRC allows up to 7.75 inches rise and requires at least 10 inches run. The ratio of rise to run should be roughly 1:1.5 for a natural stride.

Can I use a 2×6 for a stringer?

No, a 2×6 is too thin to cut notches without compromising strength. Use a 2×12 for most residential stringers. The notch should not remove more than one-third of the board’s width, so a 2×12 with a 7.5-inch rise leaves about 4.5 inches of solid wood, which is acceptable.

Do I need to subtract the tread thickness from the rise?

Yes, if you are adding treads on top of the stringer, subtract the tread thickness from the step rise when cutting the notches. For example, if your tread is 1 inch thick, cut the vertical leg of the notch to 6.5 inches instead of 7.5 inches. This keeps the final rise at 7.5 inches.

What if my total run is not a multiple of the number of steps?

That is fine. The calculator divides the total run by the number of steps, so the step run may be a decimal. You can round to the nearest 1/16 inch when marking the stringer, but keep all steps identical. If the decimal is too far from a standard tread depth, adjust the total run or the number of steps.

How many stringers do I need for a deck?

Typically, stringers are spaced 16 inches on center for a 36-inch-wide stairway, so you would need three stringers. For wider stairs, add more. The stringer calculator only computes the cut dimensions, not the number of boards.

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in total_rise | Total rise | in | 30 | 0
in total_run | Total run | in | 36 | 0
in tread | Tread depth | in | 10 | 0
out rise | Step rise | in | total_rise / round(total_rise / 7.5) | 2
out run | Step run | in | total_run / round(total_rise / 7.5) | 2
out steps | Number of steps | - | round(total_rise / 7.5) | 0