Stair Calculator
Steps equal your total rise divided by a comfortable riser height of about 7.5 inches, rounded to a whole number. Enter the total rise to get steps, riser height, run, and stringers.
How to lay out stairs
Start with the total rise — the vertical distance between the two finished levels — and divide by a comfortable riser height near 7.5 inches. Round to a whole number of steps, then the calculator divides the rise evenly so every riser is identical, which codes require.
Treads and total run
There is always one fewer tread than risers, because the top landing is the final step. Multiply the treads by your tread depth to get the total horizontal run, which tells you how far the stairs project from the structure.
Stringers
Cut stringers carry the treads. Space them about 16 inches apart — three for a standard 36-inch flight. For the deck the stairs descend from, use the deck cost calculator.
Frequently asked
How do I calculate the number of stairs?
Divide the total floor-to-floor rise by a target riser height — about 7.5 inches is comfortable — and round to the nearest whole number. That whole number is your step count.
What is a comfortable riser height?
Most codes cap risers at about 7.75 inches and require them within 3/8 inch of each other. The calculator splits your rise evenly so every step matches.
How many stringers do I need?
Space stringers about 16 inches apart, so a 36-inch stair needs 3 and a wider 48-inch stair needs 4. Heavier loads call for closer spacing.