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Concrete Stairs Calculator

Stairs look like a small job and are not. Each step sits on top of the one below, so the volume grows faster than people expect — a four-step flight holds more concrete than a slab of the same footprint. Enter the rise, run, width and step count below.

RiseRunWidthPlatform
Concrete stairs: rise, run, width and platform
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How the volume is worked out

Stairs poured against the ground are a stack of boxes. Step one is a single rise tall, step two is two rises tall, and so on to the top. The calculator adds every step:

Volume = Σ (Run × Rise × n × Width) for each step n, plus the platform if you have one.

Worked example. Four steps, 175 mm rise, 275 mm run, 1 m wide: 0.275 × 1 × 0.175 × (1+2+3+4) = 0.48 m³. That is about 1.2 tonnes of concrete for a flight most people would describe as “just a few steps”.

Step dimensions that feel right

Dimension UK typical US typical
Rise (height per step) 150–190 mm 6–7.75 in
Run / going (depth) 250–300 mm 10–11 in
Width (garden steps) 900 mm+ 36 in+
Sanity check 2 × rise + run ≈ 550–700 mm (21–27 in)

Every rise in a flight must be identical. A single step 15 mm out of line is the one people trip on, and it fails building regulations besides. Set your formwork off a level datum, not off the ground.

Saving concrete on a big flight

Solid stairs can be part-filled with compacted hardcore in the core, provided you keep at least 100 to 150 mm of concrete on every exposed face. On a wide flight that can cut the pour by a third. Engineered or cantilevered stairs are a different matter entirely — pour those to the design and do not improvise.

Whatever you fill the core with, pour the concrete in one go. A joint between steps shows up as a crack line within a couple of winters.

Frequently asked questions

How much concrete for 3 steps?

Three steps at a 7 in rise, 11 in run and 36 in wide come to roughly 0.4 yd³ (0.3 m³) poured solid — around 18 bags of 80 lb premix.

Can I fill the middle of concrete steps?

Yes, on ground-bearing steps. Compacted hardcore in the core with 100 to 150 mm of concrete cover on every face works fine and saves a lot of material.

Do concrete steps need reinforcement?

Small garden steps on solid ground usually do not. Wider flights, freeze-thaw climates and anything cantilevered need mesh or bars. Always pour the whole flight in one session.

What mix for outdoor steps?

C25, air-entrained where frost and de-icing salt are a factor. Keep the mix on the stiff side — a low slump holds the step nosing shape instead of slumping out of the form.

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