Concrete Stairs Calculator

This is an estimate, not professional advice. Check your inputs and verify the result against your plans and local building code before you build or order. See terms and disclaimer.

How this calculator works

Enter your dimensions and the result updates instantly. A waste allowance is included so you order slightly over rather than running short mid-pour, and ready-mix is rounded up to the nearest quarter yard, which is how it is sold.

Worked example

A 3 ft wide flight of 4 steps, 7 inch rise and 11 inch run, with a 10% waste allowance. Inputs: Stair width 3 ft, Number of steps 4, Rise per step 7 in, Run (tread depth) 11 in, Waste allowance 10 %. Result: 0.65 yd³ (about 30 × 80 lb bags).

Concrete for common stair flights

Calculated 3 ft wide with a 7 inch rise, 11 inch run and 10% waste. Tap a size to load it above.

Method & assumptions

This estimates poured concrete stairs two ways. The solid option, the kind formed against the ground and filled solid, is a stepped wedge whose area is the run times the rise times the staircase series, steps times steps-plus-one over two, which accounts for each step sitting on the solid below it. The suspended slab option is for a flight that spans between landings rather than sitting on the ground: there the concrete is a constant-thickness sloped slab, the waist, following the underside, plus the triangular steps on top, which uses much less concrete than a solid fill. Pick the one that matches how your stairs are built.

We multiply that cross-section by the stair width to get the volume, convert square inches to square feet by dividing by 144, add your waste allowance, and divide by 27 for cubic yards. Ready-mix is rounded up to the nearest quarter yard and bags are rounded up. For a small stoop, bags are usually easiest; a long flight quickly passes a cubic yard, where ready-mix wins.

Keep the steps within code: a common rule is a rise of about 7 inches and a run of at least 10 to 11 inches, with all steps equal. This figure is the solid stair concrete plus an optional top landing slab, if you set a landing depth and thickness. It does not include a thickened edge or the rebar most stairs carry, which you can size with our rebar calculator. Confirm the design against local code, especially the rise, run and any required handrail.

Pro tips and common mistakes

• Keep every step equal. Uneven risers are a trip hazard and often a code violation. Lay out the total rise and divide it evenly before you build the forms.
• Build strong forms. Wet concrete pushes hard on stair forms. Brace the risers and sides well, because a blown form mid-pour ruins the steps and wastes the load.
• Add rebar and a key. Most stairs carry rebar and tie into the slab or footing below with a keyway or dowels. Size the steel with our rebar calculator so the stairs do not crack or slide.
• Pour from the bottom up. Fill the bottom step first and work up, rodding each step to fill voids. Working top-down lets the lower steps slump out of the forms.
• Finish for grip. Broom or trowel a non-slip texture across the treads and slope them a hair forward to shed water. Smooth troweled stairs get dangerous when wet.

Frequently asked questions

References

• Stairs (Wikipedia)
• ACI 332: Residential concrete code
• QUIKRETE Concrete Mix yield (spec sheet)

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