Concrete Stairs Calculator

1. Enter the number of steps in your staircase.
2. Set the rise per step in inches (the vertical height of each step).
3. Set the tread depth in inches (the horizontal surface of each step).
4. Enter the stair width in inches.
5. Enter the landing depth in inches, or 0 if there is no top landing.
6. Set the base slab thickness in inches (the concrete under the stair profile).
7. Read the total concrete volume in cubic feet and cubic yards, plus bag counts.

Concrete stairs are a solid, poured structure that connects two levels. Unlike wood or steel stairs that sit on stringers, concrete stairs are a monolithic mass of cured concrete formed in a stepped shape. They are common for front porches, basements, garages and commercial entries.

The concrete fills the entire stepped profile from the base slab to the top of each tread. A top landing, when present, is a flat slab at the full height of the last step. Rebar or wire mesh is typically placed inside the forms before the pour for tensile strength.

Because concrete stairs are solid rather than hollow, they use more material than many builders expect. An accurate volume estimate prevents both costly over-ordering and mid-pour shortages. See the construction calculators hub for more building tools.

The calculator models the stair cross-section as a series of stacked rectangles, then multiplies by the stair width to get volume.

Why the Formula Uses N X (n + 1) / 2

Each step from bottom to top is progressively taller. Step 1 has a height of one rise, step 2 has two rises, and so on up to step n. The sum 1 + 2 + ... + n equals n x (n + 1) / 2. Multiplying by tread and rise gives the total stepped area above the base slab.

Bag Counts

An 80 lb bag of premixed concrete yields about 0.6 cu ft. A 60 lb bag yields about 0.45 cu ft. The calculator divides the total volume by the per-bag yield and rounds up.

Calculate the concrete for 4 steps, each 7.5 in rise and 11 in tread, 48 in wide, with a 36 in landing and a 4 in base slab.

Step 1: Convert to Feet

Width = 48 / 12 = 4 ft. Tread = 11 / 12 = 0.9167 ft. Rise = 7.5 / 12 = 0.625 ft. Slab = 4 / 12 = 0.3333 ft. Landing = 36 / 12 = 3 ft.

Step 2: Stair Cross-Section Area

A = 0.9167 x 0.625 x 4 x 5 / 2 + 4 x 0.9167 x 0.3333 = 5.7292 + 1.2222 = 6.9514 sq ft.

Step 3: Stair Volume

V_stair = 4 x 6.9514 = 27.81 cu ft.

Step 4: Landing Volume

Total rise = 4 x 0.625 = 2.5 ft. V_land = 4 x 3 x (2.5 + 0.3333) = 4 x 3 x 2.8333 = 34.0 cu ft.

Step 5: Total

V_total = 27.81 + 34.0 = 61.81 cu ft = 61.81 / 27 = 2.29 cu yd.

80 lb bags: ceil(61.81 / 0.6) = 104 bags. 60 lb bags: ceil(61.81 / 0.45) = 138 bags.

For a pour this size most builders would order ready-mix by the yard rather than hand-mix over 100 bags.

The 2021 International Residential Code (IRC R311.7) sets minimum and maximum dimensions for residential stairs.

The calculator flags a warning when the rise exceeds 7.75 in, the tread is under 10 in, or the width is under 36 in. Local codes may impose stricter rules, so check with your building department before pouring.

Small jobs can be mixed by hand with bagged concrete. Larger pours are more practical with ready-mix delivered by truck.

When to Switch to Ready-Mix

Hand-mixing more than about 50 to 60 bags is slow and exhausting. For a 4-step staircase with a landing (roughly 2 cu yd), ready-mix is usually the better choice unless access is limited. Most plants have a minimum order of 1 cu yd and a short-load fee under 3 to 4 cu yd.

Waste Factor

Order 5 to 10 percent more concrete than the calculated volume. Some concrete sticks to the mixer, and forms are never perfectly tight. The calculator shows the theoretical volume; add the waste buffer yourself.

Form Construction

Build sturdy forms from 2x lumber or plywood. The forms must resist the lateral pressure of wet concrete without bulging. Brace the sides well and seal joints with foam tape or caulk to prevent bleed-through.

Rebar Layout

Place rebar or welded wire mesh in the lower third of the slab and along the risers. A common residential layout is No. 4 rebar on 12-inch centers running both directions, with bars bent up into the risers. See the rebar calculator for spacing and weight.

Pouring Sequence

Pour from the bottom step upward. Vibrate or tamp each step to consolidate the concrete and remove air pockets. Screed each tread flat before moving to the next step. Work quickly because stair concrete starts setting before you finish the top.

Finishing

After screeding, use a mag float for a smooth surface and a broom finish for slip resistance. Round the nosing edges with an edging tool. Trowel the landing the same way you would a standard slab.

Curing

Keep the concrete moist for at least 7 days. Cover with plastic sheeting or apply a curing compound. Do not strip the riser forms for at least 24 to 48 hours.

Several variables change how much concrete a staircase actually needs beyond the basic geometry.

Step Dimensions

A taller rise or deeper tread increases the cross-section area and the volume per step. Even a half-inch change in rise, multiplied across many steps, shifts the total noticeably.

Landing Size

A wide, deep landing at the top of the stairs can account for more than half of the total concrete. Reducing or eliminating the landing saves material when the design allows it.

Base Slab Thickness

A thicker base slab adds volume under the entire run and landing. Going from 4 inches to 6 inches on a 4-step staircase can add several cubic feet.

Stair Width

Width is a straight multiplier. A 60-inch-wide staircase uses 25 percent more concrete than a 48-inch one with the same profile.

Waste and Overages

Form leaks, tool cleanup and over-filling add 5 to 10 percent to the theoretical volume. Always order extra.

Planning a New Pour

Before ordering concrete or bags, run the calculator to know exactly how much material the job needs. An accurate estimate prevents expensive short pours and excessive leftovers.

Comparing Bags vs Ready-Mix

Enter your dimensions and look at the bag count. If it exceeds 50 or so bags, ready-mix delivery is almost always faster and cheaper.

Checking Code Compliance

The calculator flags rise, tread and width values that fall outside IRC residential limits, giving you a quick sanity check before you submit plans.

Budgeting Material Cost

Multiply the bag count by the price per bag, or the cubic yards by the per-yard ready-mix rate, to build a material budget line for the project.

1. Forgetting the Triangular Buildup

Concrete stairs are solid. Each step from bottom to top is taller than the last. Treating every step as the same height underestimates the total by a large margin.

2. Ignoring the Landing

The landing slab sits at the full height of the staircase plus the base slab. On a 4-step set with a 3-foot landing, the landing alone can be more than half the total volume.

3. Skipping the Base Slab

Even a 4-inch base under the stair run adds meaningful volume. Leaving it out of the estimate means ordering too little concrete.

4. Using the Wrong Bag Yield

An 80 lb bag yields 0.6 cu ft, not 0.8. A 60 lb bag yields 0.45 cu ft, not 0.6. Using the wrong number throws off the bag count.

5. Not Adding a Waste Factor

The calculator gives the theoretical volume. Real pours always need 5 to 10 percent more for spillage, form leaks and cleanup.

The math is exact for the geometric model used, but real pours have variables the calculator does not capture.

It depends on the number of steps, rise, tread, width, landing and slab thickness. Enter your dimensions above. A typical 4-step staircase with a 3-foot landing and 4-inch base needs about 62 cu ft (2.3 cu yd).

Find the cross-section area of the stepped profile: tread times rise times n times (n+1) divided by 2, plus n times tread times slab thickness. Multiply by stair width, then add the landing volume.

For 4 steps at 7.5 in rise, 11 in tread, 48 in wide with a 36 in landing and 4 in slab, you need about 104 bags of 80 lb mix or 138 bags of 60 lb mix (roughly 2.3 cu yd total).

For small stairs (under about 1.5 cu yd), bags are workable. Larger pours of 2 cu yd or more are faster and easier with ready-mix delivered by truck.

The IRC R311.7 (2021) sets a maximum riser height of 7.75 inches for residential stairs. Many builders use 7 to 7.5 inches for comfort.

The IRC requires a minimum tread depth of 10 inches. An 11-inch tread is a common choice that meets code and feels comfortable.

Yes. Concrete is strong in compression but weak in tension. Rebar or welded wire mesh placed in the lower portion of the stairs prevents cracking and structural failure.

A 4-inch base slab is standard for residential stairs. Heavier-duty or commercial stairs may need 5 to 6 inches. The base must rest on compacted fill or undisturbed soil.

Order 5 to 10 percent more than the calculated volume. Some concrete is lost in the mixer, on tools and through form joints. Running short during a pour is costly.

No. This calculator is for straight-run stairs with uniform step dimensions. Curved or spiral stairs require a different geometric model.

• 2021 International Residential Code (IRC) R311.7 (International Code Council; stairway requirements including maximum rise, minimum tread depth and minimum width).
• Portland Cement Association - Concrete Basics (PCA; concrete volume estimation and mix design fundamentals).
• Quikrete concrete yield data (Quikrete; 60 lb bag yields 0.45 cu ft, 80 lb bag yields 0.6 cu ft of cured concrete).