How much concrete do I need for 3 steps?

For a typical flight of three steps 48 inches wide with a 7 inch rise and 11 inch tread, about 12.8 ft³ or 0.36 m³ of concrete — roughly 24 bags of 80 lb once you allow 10% for wastage. The width matters as much as the step count: the same three steps at 36 inches wide drop to about 9.6 ft³. If you have a landing at the top, add its depth multiplied by the total rise and the width, which grows the total quickly.

Why is the volume more than half the bounding box?

Because a staircase is not a wedge. If you draw a flight in side elevation and then draw the triangle from the bottom front corner to the top back corner, the steps stick out above that line by half a rise at every tread. Counting properly, the cross-section is the triangular number of the step count — n(n+1)/2 rise-by-tread rectangles — rather than half of n². For three steps that is 6 rather than 4.5, so the wedge shortcut is 25% short. For six steps it is 21 rather than 18, still 14% short.

What is the maximum rise and minimum tread for steps?

Under the International Residential Code, which most of the United States follows, the maximum riser height is 7¾ inches and the minimum tread depth is 10 inches. Risers within a single flight must not vary by more than ⅜ inch between the tallest and shortest, which matters more than people expect — the foot learns the rhythm of a staircase after two steps and an odd one catches it out. Other countries differ substantially: UK Building Regulations Part K allows a 220 mm rise on private stairs with a 220 mm going, which would fail an American inspection.

What is the 2R + T rule?

Two rises plus one tread should come to between 24 and 25 inches, or roughly 600 to 640 mm. It is one of the oldest rules in building, attributed to the seventeenth-century architect François Blondel, and it approximates the length of a comfortable human pace on an incline. A 7 inch rise with an 11 inch tread gives exactly 25 inches, which is why that combination is so common. Steps outside the band feel wrong even when every dimension is legal — too low a figure makes you mince, too high and you are stretching for each tread.

Should I fill the middle with rubble instead of concrete?

On a large flight, yes, and it is standard practice. Building a compacted core of clean hardcore or gravel and pouring a concrete shell around it saves a substantial amount of material on a tall set of steps, where the interior mass is doing very little structural work. The shell needs to be thick enough to carry the load and resist frost — commonly four to six inches — and the core must be genuinely compacted in layers, because any settlement later shows as a cracked tread. For anything up to about three steps it is usually simpler to pour solid.

Do concrete steps need reinforcement?

Yes for anything beyond a single step. Steel reinforcement does not stop concrete cracking, but it holds the pieces together and transfers load across a crack once one forms, which is the difference between a hairline you paint over and a corner that breaks away. Use rebar or mesh set clear of the forms and lifted off the base on chairs so it sits within the concrete rather than resting on the ground, where it does nothing and rusts. Tie the steps to any adjoining slab or foundation with dowels so the two move together.

How thick should the footing under the steps be?

The steps need to bear on ground that will not move, which in practice means a compacted base below the frost line for your area. In a mild climate a well-compacted gravel base of 4 to 6 inches under the whole footprint may be enough. Where the ground freezes deeply, the steps need a proper footing taken down below the frost line, or they will be lifted a little every winter and will pull away from the building. Steps that heave away from a doorway are one of the most common concrete failures in cold climates.

Should the treads slope?

Slightly, yes — about a quarter inch of fall per foot of tread depth, sloping forward and away from the building. Flat treads hold water, and water sitting on a tread freezes into an invisible sheet or works its way into the surface and spalls it over successive winters. The fall is small enough that nobody notices it underfoot but large enough that rain runs off rather than pooling. Finish the surface with a broom drawn across the direction of travel, since a smooth troweled tread is dangerously slick when wet.

Is it cheaper to mix bags or order ready-mix?

Below about half a cubic metre, bags win on convenience and there is no minimum charge. Above roughly a cubic metre — around 35 ft³, or a four-step flight at typical dimensions — bags stop making sense. You are mixing forty or more of them by hand, which is most of a day, and the cost per cubic metre is usually higher than delivered ready-mix once you count it honestly. There is also a quality argument: a flight poured continuously from one load is monolithic, whereas one built up from batches mixed over several hours has cold joints between courses that are permanent weak planes.

Concrete Steps Calculator

Concrete steps look like the simplest possible volume problem and they are one of the easiest to get badly wrong. The instinctive shortcut is to imagine the flight as a wedge — half of the box it sits inside — and that reliably under-orders, sometimes by a third. A flight of steps is not a triangle....

THE FLIGHT

NUMBER OF STEPS

WIDTH (in)

RISE PER STEP (in)

TREAD DEPTH (in)

TOP LANDING DEPTH (in) — 0 IF NONE

CONCRETE TO BUY

24 bags

23.5 exact · 80 lb each · yields 0.600 ft³ per bag

CONCRETE

14.117 ft³

TOTAL RISE

21 in

TOTAL RUN

33 in

Solid volume

12.833 ft³

After core fill

12.833 ft³

With 10% wastage

14.117 ft³

Also equals

0.400 m³

Steps

3 × 7 in rise

Tread depth

11 in

Total rise

21 in

2 × rise + tread

25 in

BUILDING THEM

Excavate below the frost line and compact a gravel base. The flight rises 21 in over 33 in of ground.

Build the form with 3 riser boards at 7 in, braced hard — wet concrete pushes outward with real force and a bowed riser board shows forever.

Set reinforcement clear of the form and off the base, then pour from the bottom step upward so each course supports the one above it.

Pour 14.117 ft³ in total. Float the treads with a slight fall forward so water runs off, and broom the surface across the direction of travel for grip.

THE FLIGHT

Why steps are not a wedge. The obvious shortcut is to treat the flight as half its bounding box, and it under-orders every time. Counting from the bottom, each course is one tread longer than the one above it, so the cross-section is 3 × 4 ÷ 2 = 6 tread-by-rise rectangles rather than half of 9. For this flight that is 12.833 ft³ in the steps.

Two rises plus one tread is the oldest rule in stair design — it approximates the length of a comfortable pace, and steps that fall outside the band feel wrong underfoot even when every individual dimension is legal.

Live calculation · updates as you type

Created with❤️byeaglecalculator.com

HOW TO USE

1
Enter how many steps the flight has and how wide it is. Width is the full width of the concrete, not the walking surface, so include any side cheeks you intend to pour as part of the same mass.
2
Set the rise per step and the tread depth. The calculator flags a riser over 7¾ inches or a tread under 10 inches, and shows where two rises plus a tread falls against the 24 to 25 inch comfort band.
3
Add a top landing depth if the flight finishes in a platform rather than meeting an existing slab. Leave it at zero if the top step arrives directly at the door threshold.
4
Read off the bags. Open site adjustments to change the wastage allowance, pick a different bag size, or enter a core fill percentage if you are building a rubble core rather than pouring the whole mass solid.

THE FORMULAS

Cross-section of flightrise × tread × n(n+1)/2

Landing cross-sectionlanding × total rise

Solid volumewidth × (flight + landing)

After core fillsolid × (1 − fill%)

With wastagenet × (1 + waste%)

Bags requiredvolume / bag yield

Total risen × rise

Comfort rule2 × rise + tread = 24–25 in

COMMON FLIGHTS

Steps	Rise × tread	Width	Total rise	Concrete	80 lb bags
1	7″ × 11″	36″	7″	1.60 ft³	3
2	7″ × 11″	48″	14″	6.42 ft³	12
3	7″ × 11″	48″	21″	12.83 ft³	24
4	7″ × 11″	48″	28″	21.39 ft³	40
5	7″ × 11″	60″	35″	40.10 ft³	74
6	7″ × 11″	60″	42″	56.15 ft³	103

Bag counts include a 10% wastage allowance and assume a solid pour with no core fill. Notice how steeply the volume climbs — six steps is not twice four, it is nearly twice again, because each course added is longer than every one above it.

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Last updated: July 28, 2026 · Formula verified · Eagle-eyed accuracy for every calculation.