Building deck stairs, basement steps, or a new staircase? Just enter your total rise and desired step dimensions, and our free stair calculator gives you the exact number of steps, rise per step, run depth, stair angle, and stringer length. It even checks your numbers against building codes so your stairs are safe and comfortable.
Modify the values and click the calculate button to use
| 16th | 8th | 4th | 2nd | Decimal |
|---|---|---|---|---|
| 1/16 | 0.0625 | |||
| 2/16 | 1/8 | 0.125 | ||
| 3/16 | 0.1875 | |||
| 4/16 | 2/8 | 1/4 | 0.25 | |
| 5/16 | 0.3125 | |||
| 6/16 | 3/8 | 0.375 | ||
| 7/16 | 0.4375 | |||
| 8/16 | 4/8 | 2/4 | 1/2 | 0.5 |
| 9/16 | 0.5625 | |||
| 10/16 | 5/8 | 0.625 | ||
| 11/16 | 0.6875 | |||
| 12/16 | 6/8 | 3/4 | 0.75 | |
| 13/16 | 0.8125 | |||
| 14/16 | 7/8 | 0.875 | ||
| 15/16 | 0.9375 | |||
| 16/16 | 8/8 | 4/4 | 2/2 | 1 |
Common fractions converted to their decimal equivalents for easy reference
A stair calculator is a tool that figures out all the dimensions for a set of stairs. You give it the total height (rise) and total length (run), and it tells you:
Sounds simple, right? It is. But the magic is in the details. A good calculator saves you from making expensive mistakes. Like cutting a stringer too short. Or ending up with stairs that feel like a ladder.
Pretty much anyone building stairs. Here are the most common folks:
DIY homeowners
Building deck stairs or basement stairs.
Carpenters and contractors
Need fast, accurate numbers on the job site.
Architects and designers
Planning staircases for new homes.
Students
Learning about construction math.
No matter who you are, the goal is the same. Safe, comfortable stairs that meet building codes.
Okay, let's talk about the formula. Don't worry — it's not scary.
The two most important numbers are rise and run.
⬆️ Rise
The vertical height of each step
➡️ Run
The horizontal depth of each step (where your foot lands)
There's a simple rule that most builders follow. It's called the 7-11 rule. The ideal rise is about 7 inches, and the ideal run is about 11 inches. But here's the thing — that's just a starting point. Building codes allow a range.
The actual formula:
Number of steps = Total rise ÷ Ideal rise height
Let's say your total rise (from the ground to the top of the deck) is 70 inches. And you want a rise of 7 inches per step. 70 ÷ 7 = 10 steps.
But what if it doesn't divide evenly? Say your total rise is 73 inches. 73 ÷ 7 = 10.42. You can't have half a step. So you round up to 11 steps, then divide 73 by 11. That gives you a rise of about 6.64 inches per step. That's totally fine.
Once you know the number of steps, figure out the total run. Multiply the number of steps by the run depth. If your run is 11 inches and you have 10 steps, your total run is 110 inches. See? Not so bad.
Using our calculator is dead simple. Here's what you do:
Measure the total rise. This is the vertical distance from the bottom floor to the top floor. Use a tape measure. Be precise.
Measure the total run. This is the horizontal distance the stairs will cover. If you're not sure, leave it blank and the calculator will figure it out based on your rise.
Enter your desired rise and run. Most people start with 7 inches for rise and 11 inches for run. But you can adjust these.
Hit calculate. The calculator gives you the number of steps, the exact rise and run per step, the angle, and the stringer length.
That's it. You now have a complete blueprint for your stairs.
Deck 60 inches off the ground. Ideal rise 7 inches. Calculator says 9 steps (60 ÷ 7 = 8.57, rounded up). Each step rise = 6.67 inches. Run = 11 inches, total run = 99 inches. Stringers about 115 inches long.
Basement floor 96 inches below. Steeper stairs to save space — rise set to 7.5 inches. Calculator says 13 steps (96 ÷ 7.5 = 12.8). Each step rise = 7.38 inches. Run = 10 inches, total run = 130 inches. Steep but works in tight spaces.
Old house with uneven stairs. Total rise = 84 inches. Want 7 inch rises. Calculator says 12 steps. Now you know exactly how to rebuild so every step is the same height.
Mistake 1: Uneven Riser Heights
This is the number one code violation. Every step should have the exact same rise. If one step is 7 inches and the next is 7.5 inches, someone will trip. The human brain expects consistency. Measure carefully.
Mistake 2: Cutting Stringers Too Deep
When you notch a stringer, you're cutting away wood. Cut too deep, and the stringer becomes weak. It can crack under weight. Leave at least 3.5 inches of solid wood at the back. Our calculator tells you the exact notch depth.
Mistake 3: Ignoring Building Codes
Building codes exist for a reason. Most codes say rise between 4 and 7.75 inches. Run at least 10 inches. Angle between 30 and 50 degrees. Check your local codes before cutting.
Mistake 4: Not Accounting for Tread Thickness
If you're adding treads (the boards you walk on), they add height. A 1-inch thick tread means your first step is 1 inch higher than calculated. Our calculator has an option for tread thickness.
The stringer is the angled board that supports the steps. It's usually a 2×12 piece of lumber. You cut notches into it to hold the treads and risers.
Here's the key. The stringer length is not the same as the total run. It's the diagonal distance from the top to the bottom. Our calculator uses the Pythagorean theorem to figure this out. It's the square root of (total rise² + total run²).
So if your total rise is 70 inches and total run is 110 inches, the stringer length is about 130 inches. That's a 10-foot 10-inch board. Make sure you buy lumber long enough.
Codes vary by location, but here are the common rules:
Always check with your local building department. They might have different rules.
🏠 Interior Stairs
Usually steeper — rise of 7 to 7.75 inches, run of 10 to 11 inches. Built with finished wood and often have handrails on both sides.
🌳 Exterior Stairs
Usually shallower — rise of 6 to 7 inches, run of 11 to 12 inches. More room for carrying things. Built with pressure-treated lumber to resist rot.
This is a common problem, especially in older homes. If your stairs feel like a ladder, you have a few options:
Rebuild them.
This is the best solution, but it's a lot of work.
Add a landing.
If you have enough space, split the stairs into two shorter flights with a landing in between. This makes them less steep.
Change the angle.
If you can extend the run, you can reduce the rise. But this requires more floor space.
Our calculator can help you explore different options. Just change the rise and run numbers and see what happens.
Here's something most people don't know. The first step and the last step are often different from the rest. Why? Because the floor at the top and bottom might not be perfectly level. You might need to adjust the first or last riser by a tiny amount to make everything work.
Another tip. Always build a temporary stringer first. Cut it, test it, and make sure it fits. Then use it as a template for the rest. This saves you from ruining expensive lumber.
And here's a fun fact. The word "stair" comes from the Old English word "stæger," which means "to climb." People have been building stairs for thousands of years. The ancient Romans had concrete stairs. The Egyptians used stone. We're just using better tools now.
Look, we love DIY. But stairs are dangerous if done wrong. If you're not confident in your measurements or your carpentry skills, hire a professional. A bad set of stairs can cause serious injuries. It's worth the money to get it right.
That said, our calculator gives you the confidence to plan your project. You'll know exactly what materials you need and how to cut them. That's half the battle.
The part you step on. Minimum 10 inches (25.4 cm).
Height of each step. Maximum 7.75 inches (19.7 cm).
Protrusion at tread edge. 0.75-1.25 inches (1.9-3.2 cm).
Height from tread to ceiling. Minimum 6 ft 8 in (203.2 cm).
Edge to edge of tread. Minimum 36 inches (91.44 cm).
34-38 inches high, 1.25-2.675 inch diameter.
Measure the total rise from the bottom floor to the top floor. Divide that number by your desired rise height (usually 7 inches). Round up to the nearest whole number. That's your number of steps. For example, if your total rise is 70 inches, 70 ÷ 7 = 10 steps.
The most common rule is the 7-11 rule. That means a 7-inch rise and an 11-inch run. But building codes allow a range. The rise can be between 4 and 7.75 inches. The run should be at least 10 inches. Always check your local codes.
Use a tape measure. Measure the vertical distance from the floor where the stairs will start to the floor where they will end. For deck stairs, measure from the ground to the top of the deck. Be as precise as possible. Even a quarter-inch error can cause problems.
A stair stringer is the angled board that supports the steps. Its length is the diagonal distance from the top to the bottom of the stairs. You can calculate it using the Pythagorean theorem: square root of (total rise² + total run²). Our calculator does this for you.
Uneven stairs are usually caused by inaccurate measurements or cutting errors. The fix is to rebuild them with consistent rise and run. Every step should be exactly the same height. Use our calculator to get precise numbers, and measure twice before cutting.
Building codes require a minimum of 6 feet 8 inches (80 inches or 203.2 cm) of headroom measured vertically from the stair tread to the ceiling above. Anything less is a safety hazard.
The stair angle is calculated using the inverse tangent: arctan(total rise ÷ total run). Our calculator does this automatically. Most comfortable stairs have an angle between 30 and 37 degrees.
Building codes typically require a landing for stairs with more than 12 feet of vertical rise. Landings must be at least as wide as the stairs and at least 36 inches deep in the direction of travel.
Use 2×12 pressure-treated lumber for exterior stairs and 2×12 kiln-dried lumber for interior stairs. Always inspect boards for knots, cracks, or warping before cutting — defects can weaken the stringer.
Mark the rise and run on the stringer using a framing square and stair gauges. Cut along the lines with a circular saw, finishing the corners with a handsaw. Never overcut — it weakens the stringer. Use the first stringer as a template for the rest.
Closed stringers have the treads and risers housed in routed slots — common in finished interior stairs. Open (cut) stringers have notches cut out and the treads sit on top — common for deck and basement stairs.
DIY deck stairs typically cost $100-$300 for lumber and materials. Interior finished stairs cost $1,000-$3,000+. Professional installation adds $500-$2,000 in labor depending on complexity.
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