Staircase Concrete Calculation: Waist Slab, Steps and Landing in m³ and cft

A dog-legged staircase for a house with 3.15 m (about 10 ft 4 in) between floors, 1 m wide with a 150 mm waist slab, takes about 1.43 m³ (50.5 cft) of concrete. In M20 that is roughly 11.5 bags of cement, 0.60 m³ of sand and 1.20 m³ of stone aggregate.

A staircase concrete calculation adds up three shapes: the sloping waist slab under the steps, the small triangle of concrete in every step, and the flat landing. Each one has a simple formula. The mistakes come from measuring the slope the wrong way, counting one step too many, or counting a landing twice, and this guide shows where each one creeps in.

There are no rupee figures here. Cement and sand prices change every season. The geometry of a stair does not.

What is the formula for staircase concrete calculation?

Concrete in a staircase = waist slab + steps + landing, worked out flight by flight. A flight is one straight run of steps between two landings. A dog-legged stair, the common type in Indian houses, has two flights that turn back on each other at a mid landing.

1. Waist slab = inclined length × width of the stair × waist thickness. The waist is the sloping slab that carries the steps.
2. Steps = ½ × riser × tread × width × number of treads. The riser is the height of one step; the tread is the flat part you put your foot on.
3. Landing = length × width × thickness, like any flat slab.

Work every dimension in metres for an answer in cubic metres (m³), or in feet for cubic feet (cft). One cubic metre is 35.31 cft.

Reading the figure

• 1, dark grey: the waist slab, a sloping slab of even thickness.
• 2, light grey: the triangle of concrete in each step, sitting on top of the waist.
• 3: the landing slab where the flight ends.
• R is the riser and T the tread of one step. The orange line shows how the waist thickness is measured.

The triangle formula works because the top face of the waist runs through the inside corner of every step, so what sits above it is a row of right-angled triangles, each half of riser × tread in section. This is also how IS 456 defines the depth of a stair for design: clause 33.3 takes it as the minimum thickness measured perpendicular to the soffit, the underside of the slab. The waist on your structural drawing means that thickness.

How do you find the number of risers and treads?

Divide the floor-to-floor height by the riser height you want, and round up to a whole number. That gives the number of risers. Then divide the height again by that whole number to get the exact riser. For a 3.15 m height and a target of 175 mm, 3,150 ÷ 175 = 18 risers of exactly 175 mm, nine in each flight.

A flight always has one tread fewer than it has risers, because the top riser steps you onto the landing and the landing is the last tread. So each nine-riser flight has eight treads, and eight step triangles.

The step sizes are not free choices. Part 3 of the National Building Code of India 2016, clause 12.18, sets these limits:

The 12-riser limit is why so few Indian houses have a single straight stair between floors. A 3 m floor height at the largest allowed 190 mm riser still needs 16 risers, which is more than one flight may hold, so the stair has to break at a landing. The dog-legged shape does that inside a compact stair hall.

How do you calculate the inclined length of the waist slab?

Treat each flight as a right-angled triangle. The rise of the flight is one side, the going is the other, and the inclined length is the long side:

Inclined length = √(rise of flight² + going of flight²)

The rise of the flight is the number of risers × the riser height. The going is the number of treads × the tread width, measured flat. For a flight of nine 175 mm risers and eight 250 mm treads:

• Rise = 9 × 0.175 = 1.575 m
• Going = 8 × 0.25 = 2.00 m
• Inclined length = √(1.575² + 2.00²) = √6.48 = 2.55 m

On a drawing, take the rise and going from the section and do the sum. Do not scale the sloping line off a printed plan.

Worked example: concrete for a dog-legged staircase in m³ and cft

Take an ordinary two-storey house. Floor-to-floor height 3.15 m, stair width 1.0 m, risers 175 mm, treads 250 mm, waist 150 mm, two flights of nine risers each, and a mid landing 150 mm thick. The two flights sit side by side with a 100 mm gap between them, so the mid landing is 2 × 1.0 + 0.1 = 2.1 m long and 1.0 m deep. Those sizes stay inside every NBC limit in the table above.

The landing at the upper floor is left out on purpose. It is part of the floor slab, and it is already counted there.

That matches how IS 1200 (Part 2), the Indian Standard for measuring concrete work, splits a bill of quantities. Clause 4.2.1 lists “staircase including stringer beams but excluding landings” as one item and puts landings with slabs. So in a contractor’s measurement the flights and the landing turn up on two different lines, both in cubic metres. If you are checking a bill, add the two lines before comparing it with your own total.

How much cement, sand and aggregate does a staircase need?

The 1.43 m³ above is wet, finished concrete. The loose dry material you mix it from is larger, because sand fills the gaps between stones and cement paste fills the rest. Multiply by 1.54 to get the dry volume, then split it by the mix ratio. The building material calculation guide explains where 1.54 comes from and why a 50 kg cement bag counts as 0.0347 m³.

A staircase is reinforced concrete, and IS 456 Table 5 sets M20 as the lowest grade for reinforced concrete in mild exposure, with at least 300 kg of cement in every cubic metre. M20 as a nominal mix is 1 : 1.5 : 3.

576 kg of cement over 1.43 m³ is about 403 kg per cubic metre, comfortably above the 300 kg minimum. Order 12 bags, plus the site allowance set out in the guide to wastage of materials in construction.

Two cases change the mix. An outside stair open to rain falls into the moderate exposure class of IS 456 Table 3, and so does a stair in a coastal town, because the mild class leaves out coastal areas. There Table 5 asks for M25, and M25 has to be a designed mix tested with trial cubes. And the water in an M20 nominal mix is a ceiling, not a target; the water-cement ratio guide shows what extra water does to the strength.

Doing the same sum in feet

Many house sites in India still measure in feet and inches, so here is a second stair worked entirely in feet. Floor height 10 ft, width 3 ft 6 in, risers 6 in, treads 10 in, waist 6 in, mid landing 6 in thick, and a 6 in gap between the flights.

• Risers: 10 ft ÷ 0.5 ft = 20, ten in each flight, so nine treads per flight.
• Rise of flight = 10 × 0.5 = 5 ft. Going = 9 × 10 in = 7.5 ft.
• Inclined length = √(5² + 7.5²) = √81.25 = 9.01 ft.
• Waist, both flights = 2 × 9.01 × 3.5 × 0.5 = 31.5 cft.
• Steps, both flights = 18 × ½ × 0.5 × 0.833 × 3.5 = 13.1 cft.
• Mid landing = (3.5 + 3.5 + 0.5) × 3.5 × 0.5 = 7.5 × 3.5 × 0.5 = 13.1 cft.

Total: about 57.8 cft, or 1.64 m³. Multiplied by 1.54 that is 89 cft of dry material. In M20 the cement share is 89 ÷ 5.5 = 16.2 cft, and a 50 kg bag holds about 1.23 cft, so the stair needs a little over 13 bags. Sand comes to about 24.3 cft and aggregate 48.6 cft.

The 6 in riser and 10 in tread are about 152 mm and 254 mm, so this stair also passes the NBC limits for a house.

How much concrete is in one floor’s staircase? A quick table

Use this to check a contractor’s figure before you have the drawing worked through. It is the same dog-legged stair as the worked example, 3.15 m between floors with 175 mm risers and 250 mm treads, with the mid landing as thick as the waist.

Every 25 mm on the waist adds about 0.18 m³ to a 1 m stair, which is 6 to 7 cft and a bag and a half of cement. And going from a 1.0 m to a 1.2 m stair adds more than a fifth, because the landing grows in both directions. The waist thickness comes from the structural design, so take it from the drawing; this table only shows what it does to the quantity.

Why does my staircase quantity not match the contractor’s?

When two people work out the same stair and get different answers, it is nearly always one of these.

• The waist was measured straight down. A vertical cut through a sloping slab is thicker than the true waist. In the worked example the slope makes 150 mm square to the soffit read about 191 mm straight down. Vertical depth × inclined length overstates the waist by about 27%, here 0.21 m³ (7.4 cft). Use the true waist with the inclined length, or the vertical depth with the flat going. Both give the right answer; mixing them does not.
• Steps were counted by risers. Nine risers but eight treads means eight triangles. Counting nine adds one triangle per flight, 0.022 m³ each here. Small, and on the safe side, but it is why two careful sums can differ.
• A landing was counted twice. The top landing belongs to the floor slab. Count it once, in the floor.
• Only one flight was counted. A dog-legged stair has two. An open-well stair, which turns twice round an open middle, has three flights and two landings.
• Wet and dry volumes were mixed up. The 1.43 m³ is what you pour. Ordering only that much sand and stone leaves you about a third short, because the dry heap is 1.54 times bigger.

A first step that sits on the ground floor, or a bottom flight carried on its own beam, adds concrete outside this sum. Measure those separately, the way plinth beam concrete is measured.

Steel, shuttering and cover for the stair

The concrete is one part of the stair’s quantity sheet. The steel is taken off the drawing bar by bar; the cranked main bars that run up the waist and into the landing are worked out in a bar bending schedule. The cover between those bars and the soffit is held by spacers sized in the guide to cover block size for slab, beam, column and footing. The formwork is the sloping soffit, the two sides and the face of every riser, and how that work is priced is explained in shuttering rate per sqm.

A stair is narrow, steep and full of corners, so compaction matters. Poorly vibrated concrete at a riser face shows up later as the voids described in honeycombing in concrete.

Mixing the concrete for one floor’s stair

At 1.4 to 2 m³, a house stair is a small pour, and many house sites mix it on site. How site-mixed and ready-mixed concrete compare for jobs this size is covered in RMC vs site mix concrete.

A self-loading mixer picks up the ingredients with its own bucket, mixes them in its drum and carries the concrete to the stair, all in one machine. The smaller models are close to one floor’s stair in size: the Tarle SLM 2200 and the JOHN SLCM 2.2 list a 2.2 m³ drum, and the CONMAT CSLM 2800 a 2.8 m³ drum. Ask the dealer for the concrete output per batch before you plan a stair as one load.

To weigh the options, compare live concrete mixer models and prices and connect with a dealer.

The stair in the cost of a house

Once the stair is measured, it is one line of the frame estimate. The house construction cost calculator places it beside the slabs, beams and columns, and the construction estimate format guide shows where it sits in a bill of quantities. More estimating guides sit under construction cost. When you are ready to plan the pour, browse concrete mixers and talk to a dealer near your site.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication.

Code references: IS 456 : 2000 (plain and reinforced concrete, code of practice), clause 33.3 (depth of stair section measured perpendicular to the soffit), clause 9.3, Table 3 (exposure classes) and Table 5 (minimum grade M20 and 300 kg/m³ cement for reinforced concrete in mild exposure, M25 in moderate exposure); IS 1200 (Part 2) : 1974 (method of measurement, concrete works, reaffirmed 2022), clauses 4.1.2 and 4.2.1; National Building Code of India 2016, Part 3, clauses 12.18.1 and 12.18.2 (Amendment 1 of 2021 does not change them). Mixer drum capacities are as listed in the catalogue in October 2026. The worked examples are illustrations; your structural drawing decides the waist, the steps and the final quantity.