How the concrete steps calculator works
A flight of solid steps is a staircase of stacked blocks. The bottom step is one riser high, the second is two risers high, and so on, so the concrete under the treads grows like 1 + 2 + 3 + … + n. That sum equals n × (n + 1) ÷ 2, which is why four steps hold ten times the volume of a single step-sized block, not four times. A landing at the top is a slab as tall as the whole flight, so it often weighs more than all the steps together.
Volume = width × riser × tread × n(n + 1) ÷ 2 + width × landing depth × n × riser, then × 1.10The 10% allowance covers formwork that bows under the weight, an uneven sub-base and the mix left in the barrow. Bags are counted from the dry-mix yield of about 2,130 kg per cubic metre (133 lb per cubic foot), so a 25 kg bag gives roughly 11.7 litres of placed concrete and an 80 lb bag about 0.60 ft³.
Worked example
A back door sits 68 cm above the patio. Four risers of 17 cm reach it exactly. With 28 cm treads, a 1.2 m wide flight and a 0.9 m platform in front of the door:
- Steps: 1.2 × 0.17 × 0.28 × 10 = 0.571 m³
- Landing: 1.2 × 0.9 × 0.68 = 0.734 m³
- Total 1.306 m³, or 1.44 m³ with the allowance
That is about 3,060 kg of premix, or 123 bags of 25 kg. The flight projects 4 × 0.28 + 0.9 = 2.02 m from the wall. At this size, a small ready-mix load or a rented mixer saves a lot of lifting.
Concrete per flight, solid fill, no landing
| Steps | 1 m wide, 17 cm × 28 cm | 3 ft wide, 7 in × 11 in | 80 lb bags (3 ft wide, +10%) |
|---|---|---|---|
| 2 | 0.143 m³ | 4.8 ft³ | 9 |
| 3 | 0.286 m³ | 9.6 ft³ | 18 |
| 4 | 0.476 m³ | 16.0 ft³ | 30 |
| 5 | 0.714 m³ | 24.1 ft³ | 44 |
Adding one step to a flight costs more than the previous one did, because every new step sits on a taller column of concrete.
Ways to use less concrete
- Fill the core. Tall flights and big landings are often built with compacted hardcore or broken masonry in the middle and a 10–15 cm (4–6 in) concrete shell. Measure the shell separately; this calculator assumes solid concrete.
- Use a sloped soffit. Steps poured against sloping ground only need concrete above the slope, which can cut volume by a third on long flights.
- Keep risers identical. Divide the total height by the step count before building forms. A single riser that differs by more than about 1 cm (3/8 in) is a classic trip hazard.
- Slope the treads. Give each tread a fall of about 1 cm (1/4 in) towards the front so rain runs off instead of freezing in a puddle.
Codes and safety
US residential codes typically cap risers at 7¾ in and require treads of at least 10 in, and a handrail is generally required once a flight has four or more risers. Steps attached to a house, footings below the frost line and guards at raised landings are governed by your local building code; for anything structural, or where the landing is high enough to need a guard, check with the building office or an engineer before pouring.
Frequently asked questions
How much concrete do I need for 3 steps?
Three steps 4 ft wide with 7 in risers and 11 in treads hold about 12.8 ft³. With a 10% margin that is about 14.1 ft³ (0.52 yd³), or 24 bags of 80 lb.
How many bags of concrete for 4 steps?
Four solid steps 1 m wide with 17 cm risers and 28 cm treads need about 0.52 m³ including 10% waste, which is roughly 45 bags of 25 kg or 28 bags of 40 kg. A landing adds a lot more.
How thick should concrete steps be?
Solid steps are filled right through. If you use a hardcore core, keep at least 10–15 cm (4–6 in) of concrete over it on every tread and riser.
Do concrete steps need rebar?
Small solid steps on firm ground are often poured with light mesh or a few bars tying them to the slab or wall. Steps attached to a building, spanning over soft ground or carrying a raised landing should be detailed to local code.
What is the best rise and tread for outdoor steps?
Garden steps feel comfortable at 15–17 cm (6–7 in) of rise with treads of 30–35 cm (12–14 in). A common check is that twice the riser plus the tread lands between 60 and 65 cm (24–26 in).
Last reviewed: 2026-09-27 · How we calculate