Concrete Stairs Calculator

How to measure

Rise is the height of one step, run is the depth of one tread, and width is the length of the stair across. Count the steps by their risers, not by the number of treads, because the top landing is not a step. If the finished stair has a landing, enter its length, width and thickness separately.

Solid steps are filled to the ground. If the stair sits on a hollow frame or a sloped slab, the volume is much smaller than this calculator shows. Treat the result as an upper limit in that case.

The solid-stair formula

Step 1 is one rise tall, step 2 is two rises tall, and so on, because each step sits on the full height below it. The blocks are therefore 1, 2, 3, … N rises high, and their total height is the triangular number N(N+1)/2. Multiply by the run, rise and width and you have the volume of the steps.

If a landing sits at the top, add length × width × thickness for it. The landing slab is usually a separate pour or at least a separate calculation.

Formula: V = W × run × rise × N(N+1)/2 + landing, with rise and run in feet.

Worked example: three steps

Three steps at 7 in rise and 11 in run, 4 ft wide:

1. Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Rise (step height) 7 in = 0.5833 ft; Run (tread depth) 11 in = 0.9167 ft; Stair width 4 ft; Landing thickness 4 in = 0.3333 ft
2. Step blocks = W × run × rise × N(N+1)/2 = 4 × 0.9167 × 0.5833 × 6 = 12.8333 ft³
3. Total = 12.8333 ft³
4. Net volume = 12.8333 ft³ ÷ 27 = 0.4753 yd³ (× 0.0283168 = 0.3634 m³)
5. Order quantity = 0.4753 yd³ × (1 + 10%) = 0.5228 yd³ = 14.1167 ft³
6. 80 lb bags = 14.1167 ft³ ÷ 0.6 ft³ per bag = 23.53 → 24 bags (always round up)
7. Weight = 14.1167 ft³ × 150 lb/ft³ = 2,118 lb

About 0.52 yd³, or 24 bags of 80 lb. It looks small until you count that bag total, so most people use bags for three steps and a truck for six.

Worked example: four steps and a 4 × 4 ft landing

1. Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Rise (step height) 7 in = 0.5833 ft; Run (tread depth) 11 in = 0.9167 ft; Stair width 4 ft; Landing length 4 ft; Landing width 4 ft; Landing thickness 4 in = 0.3333 ft
2. Step blocks = W × run × rise × N(N+1)/2 = 4 × 0.9167 × 0.5833 × 10 = 21.3889 ft³
3. Landing = 4 × 4 × 0.3333 = 5.3333 ft³
4. Total = 26.7222 ft³
5. Net volume = 26.7222 ft³ ÷ 27 = 0.9897 yd³ (× 0.0283168 = 0.7567 m³)
6. Order quantity = 0.9897 yd³ × (1 + 10%) = 1.0887 yd³ = 29.3944 ft³
7. 80 lb bags = 29.3944 ft³ ÷ 0.6 ft³ per bag = 48.99 → 49 bags (always round up)
8. Weight = 29.3944 ft³ × 150 lb/ft³ = 4,409 lb

That comes to 1.09 yd³ with waste. Compare it with the 3-step version: one extra step plus a landing more than doubles the concrete.

What the building code usually says

Residential stair geometry is set by code. In the United States the International Residential Code commonly limits risers to 7¾ in and requires treads of at least 10 in, and steps in a flight should be uniform to within a small tolerance. Local rules vary and exterior steps may have extra requirements, so check with your building department before you set forms. Do not size steps from this page: use it only to calculate the volume of a layout you have already designed.

Mistakes to avoid

• Counting the landing as a step. N is the number of risers.
• Using the sloped finished height instead of the vertical rise.
• Forgetting a thickened edge or a footing under the bottom step. Frost can heave unsupported steps.
• Pouring solid when the design calls for a hollow, backfilled stair. Ask the designer.
• Ordering without waste. Steps are fiddly and forms leak.

Plan the rest

Stairs usually meet a slab or porch. Add the landing slab with the slab calculator and combine everything in the Pour List. Use the rebar calculator to estimate steel and the formwork guide for bracing.

Frequently asked questions