What is Staircase Calculator?

Enter your total rise and available run to get the number of steps, riser height, and tread depth for code-compliant stairs. Checks against IRC residential and IBC commercial building codes.

Enter your floor-to-floor rise in inches or centimetres and, optionally, the horizontal run you have to work with. The result gives riser height, tread depth, stair angle, stringer length and a code-compliance flag against IRC residential (max 7.75" rise, min 10" tread) and IBC commercial (max 7" rise, min 11" tread) limits.

How to use

1. Enter the total floor-to-floor height (total rise) you need to span.
2. Optionally enter the available horizontal run space to constrain the design.
3. View the calculated number of steps, individual riser height, tread depth, and stair angle with code compliance indicators.

When to use

• Designing deck stairs and confirming each riser stays under the 7.75" residential limit.
• Cutting stringers from a 2×12 and needing the exact hypotenuse length to mark.
• Reviewing a contractor's stair drawing to verify code compliance before signing off.

Result

Building stairs from ground floor to second floor with a 9-foot (108 inch) total rise — the calculator suggests 15 risers at 7.2 inches each with 10-inch treads, within IRC residential code limits of 7.75-inch max riser.

FAQ

Why does my staircase need an odd number of treads?

It doesn't have to. The relationship is: if there are N risers, there are N-1 treads, because the top landing acts as the final tread. So 14 risers means 13 treads. The calculator handles the count for you once you enter the rise.

What's the ideal riser-tread relationship?

Blondel's rule, used since the 17th century: 2×riser + tread ≈ 25 inches (or about 63 cm). A 7" riser pairs with an 11" tread, a 7.5" riser with a 10" tread. Stairs that violate this feel cramped going up or awkward stepping down.

What angle should residential stairs sit at?

Between 30° and 37° is comfortable. IRC effectively limits you to about 38° at the steep end (7.75" riser, 10" tread). Anything over 40° feels like a ladder; under 27° wastes floor space and is unusual indoors.

How long should I cut the stringer?

The stringer length the calculator shows is the hypotenuse of rise and total run. Add at least 12 inches for the bottom kick and top connection cut. Use a 2×12 minimum so you have enough material left after notching out each tread and riser.

Do I need a handrail if there are only three steps?

IRC requires a handrail on stairs with four or more risers. Three risers (two treads plus the landing) usually escape the rule, but local jurisdictions sometimes go stricter. Check before you skip the rail on an exterior deck step.

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