Concrete Stairs Calculator: Steps, Volume and Cost
Stairs aren’t a slab and they aren’t a column. Two volumes stack on top of each other: the inclined slab underneath and the triangular step wedges on top. This concrete stairs calculator handles both. Enter the total rise, the stair width, your riser and tread targets, and the slab thickness, and it returns step count, run, total volume, weight, bags, and cost.
Builders use it before forming an exterior stoop or an interior basement stair. Homeowners use it to see whether a weekend pour is realistic or whether a ready-mix truck makes more sense. The math runs on the Pythagorean length of the slab plus a wedge calculation for every tread. Change any dimension and the numbers update as you type.
How to Use the Concrete Stairs Calculator
Choose your currency from the top dropdown.
Enter the floor-to-floor rise in feet, inches, meters, centimeters, or millimeters.
Add the stair width. Three and a half feet is the common residential default.
Pick a stair type: straight or with a landing.
Set the maximum riser height you’re willing to build. The tool divides total rise by this to get the step count.
Enter the tread depth. Ten inches is the residential standard.
Set slab thickness. Six inches covers most poured stairs.
Adjust waste, density, and bag size, then add your prices.
The Summary tab shows step count, run, slab volume, steps volume, and the combined total. Detailed Breakdown lists every value the calculation passes through.
How the Concrete Stairs Calculator Formula Works
Two volumes get added together. The slab is a rectangle tilted up the slope of the stairs, and the steps are triangular wedges stacked on top of it.
Formula: Number of steps = ⌈ Total rise ÷ Max riser height ⌉
Formula: Actual riser = Total rise ÷ Number of steps
Formula: Run = (Steps − 1) × Tread depth
Formula: Slab length = √(Run² + Rise²)
Formula: Slab volume = Slab length × Width × Slab thickness
Formula: Steps volume = 0.5 × Treads × Tread depth × Actual riser × Width
Formula: Total wet volume = Slab volume + Steps volume (+ Landing volume if selected)
Formula: Bags = ⌈ Total volume with waste ÷ (Bag size in lb ÷ 133) ⌉
The step count always rounds up. A 9-foot rise with a 7-inch maximum riser needs at least 16 risers, so the tool won’t return 15. The actual riser then comes out slightly shorter than the maximum, which is what you want. Every riser ends up the same height, and the whole staircase stays within code.
Two notes on the code. First, the step wedges use a 0.5 multiplier, since each step is a right triangle in cross-section. That’s a small approximation. Real stairs taper at the bottom edge and often have a nosing overhang. Second, the landing option adds a fixed 3-foot landing pad across the full stair width, multiplied by slab thickness. It’s a rough allowance, not a custom landing you can size.
There is no 1.54 dry-volume factor applied here. Wet volume is what the tool returns, unlike a slab calculator that inflates for dry material. Add waste and the bag count covers the real-world loss.
Above 1 cubic yard, the tool recommends ready-mix. At or below, it recommends bags.
Worked Example: A 9 ft Basement Stair, 3.5 ft Wide
Say you’re pouring a basement stair with a 9 ft floor-to-floor rise. Stair width is 3.5 ft. Maximum riser is 7.25 inches. Tread depth is 10.5 inches. Slab thickness is 6 inches. Waste factor is 10%. Bag size is 80 lb. Ready-mix is $150 per cubic yard.
Total rise in inches: 9 × 12 = 108 in
Steps: ⌈ 108 ÷ 7.25 ⌉ = ⌈ 14.9 ⌉ = 15 risers
Actual riser: 108 ÷ 15 = 7.2 in, or 0.6 ft
Treads: 15 − 1 = 14
Run: 14 × 0.875 ft = 12.25 ft
Stair area in plan: 12.25 × 3.5 = 42.88 ft²
Slab length: √(12.25² + 9²) = 15.20 ft
Slab volume: 15.20 × 3.5 × 0.5 = 26.60 ft³
Steps volume: 0.5 × 14 × 0.875 × 0.6 × 3.5 = 12.86 ft³
Total wet volume: 39.46 ft³
With 10% waste: 43.41 ft³, or 1.608 yd³
Concrete weight: 43.41 × 145 = 6,294 lbs (about 2,855 kg)
Yield per 80 lb bag: 0.6015 ft³
Bags needed: 43.41 ÷ 0.6015 = 72.2, rounded to 73
Cost using bags: 73 × $6.50 = $474.50
Cost using ready-mix: 1.608 × $150 = $241.20
Recommended: Ready-Mix Delivery
The volume clears one cubic yard, so ready-mix wins. Seventy-three bags is a lot of mixing, and the price gap is almost two to one. If the truck can’t reach the stair location, a pump fee changes the comparison quickly.
