Aggregate Size in Concrete: 10, 20 and 40 mm and Where Each Goes

Indian concrete is built from four aggregate sizes in practice: 10 mm, 20 mm, 40 mm and, for mass work, 63 mm. The aggregate size that suits a job is set by two numbers on the drawing, the thinnest part of the member and the gap between its steel bars, and for most house and building work that answer is 20 mm.

A stone crusher sells the same rock in several sizes, and the names on the quarry board (“20 mm metal”, “10 mm jelly”, “40 mm”) are the same names the Indian standard uses. What the names do not tell you is how much of the heap is really that size, which one a slab or a footing should get, and why the small “6 mm” chips you are offered are not a size the standard recognises at all.

This guide answers those questions from the two standards that govern them: IS 383:2016, coarse and fine aggregate for concrete, which defines the sizes, and IS 456:2000, the code for plain and reinforced concrete, which says where each one may go. Sand and quarry dust (the material below 4.75 mm) have their own page on quarry dust and M-sand grading zones; this one covers the stone above it.

What does “20 mm aggregate” actually mean?

It means stone of which 85 to 100 per cent passes a 20 mm sieve. It does not mean every piece is 20 mm across. IS 383 calls this the nominal size, the size most of the material passes, and it allows a set share of smaller stone in every load.

The dividing line between sand and stone is the 4.75 mm IS sieve. Aggregate most of which passes 4.75 mm is fine aggregate; aggregate most of which is held back by it is coarse aggregate. Everything on this page sits above that line.

IS 383 lists six single-sized nominal sizes: 63, 40, 20, 16, 12.5 and 10 mm. Single-sized means the crusher has screened the stone into one band. Table 7 of the standard sets how much of each band may be smaller than the name says.

Read the 20 mm row the way a site engineer would. Every stone in the load must pass a 40 mm sieve. At least 85 per cent must pass 20 mm. Up to a fifth may be smaller than 10 mm, and no more than 5 per cent may be sand-sized. A heap that is a third chips is not 20 mm aggregate, whatever the challan says.

The test that settles it is a sieve analysis to IS 2386 (Part 1). Any materials-testing lab can run it, and it is fair to ask the crusher for a recent report before you order a full load.

Which aggregate size is used for slab, beam, column and footing?

For most of them, 20 mm. IS 456 clause 5.3.3 says the nominal maximum size of coarse aggregate should be as large as possible, but never more than one-fourth of the minimum thickness of the member, and that “for most work, 20 mm aggregate is suitable”. It allows 40 mm or larger where nothing restricts the flow of concrete into the section, and it asks you to consider 10 mm for thin sections, closely spaced steel or small cover.

The one-quarter rule is simple arithmetic. Multiply the stone size by four and you get the thinnest member it can go into.

The thinnest member each size can go into

Minimum member thickness = 4 x nominal maximum aggregate size (IS 456:2000, clause 5.3.3). Bars drawn to scale.

The steel sets a second limit. Clause 26.3.2 asks for a clear horizontal gap between parallel main bars of at least 5 mm more than the nominal maximum aggregate size, or the bar diameter if that is larger. In heavily reinforced members, such as the ribs of main beams, clause 5.3.3.1 goes further: the stone should be 5 mm smaller than both the clear gap between main bars and the cover to the steel, whichever is smaller.

Put the two rules together and most of a house falls into place.

The thicknesses in the second column are common site figures, not code values; always work from the thickness on your own drawing. The row worth stopping on is the PCC bed. The one-quarter rule says a 100 mm bed can take stone no larger than 25 mm, and 40 mm stone needs a bed of at least 160 mm. If a schedule calls for 40 mm stone in a thinner bed, ask the engineer to confirm it before the tipper arrives.

Cover matters for the same reason. If you are fixing cover to slab or column steel, the cover block sizes for slab, beam and column are set out separately; a stone larger than the cover cannot get between the bar and the formwork.

Does a bigger aggregate size save cement?

Yes, a little, and IS 456 puts a number on it. Bigger stone has less surface to coat, so it needs less cement paste. Table 6 of the code adjusts the minimum cement content (which is written for 20 mm stone) by aggregate size.

So 10 mm concrete costs you more cement for the same durability, and 40 mm concrete saves some, but only where the member is thick enough to take it. Picking 40 mm for a thin bed to save cement swaps a small saving for a breach of the one-quarter rule.

The third column shows the other side of the trade. With smaller stone you need relatively more sand to fill the gaps; with larger stone, less. If you are working out how many cubic metres of each to order, the building material calculation for cement, sand and aggregate walks through the dry-volume sum.

What is graded aggregate, and do you need it?

Graded aggregate is stone with a planned spread of sizes, from the largest down to just above sand, so the small stones fill the gaps between the big ones. Single-sized aggregate is one band. IS 383 lists graded aggregate in four nominal sizes: 40, 20, 16 and 12.5 mm.

The difference shows at the 10 mm sieve. Single-sized 20 mm may have only 0 to 20 per cent passing 10 mm. Graded 20 mm needs 25 to 55 per cent passing 10 mm, with 90 to 100 per cent passing 20 mm and no more than 10 per cent passing 4.75 mm. One heap of 20 mm stone on its own is too coarse to be graded aggregate. That is why sites buy 20 mm and 10 mm separately and blend them.

There is no fixed blending ratio in the standard. The right share of 10 mm depends on how the two loads actually grade, which a sieve analysis of each will show. IS 456 is clear on the outcome it wants: its note to the nominal mix table says “graded coarse aggregate shall be used”, and clause 5.3.4 says coarse and fine aggregate shall be batched separately. On a site without a batching plant, a self-loading concrete mixer with a weighing bucket does that batching for you; more on that below.

What are 6 mm chips and mass-concrete sizes?

IS 383 has no 6 mm size. Its smallest single-sized coarse aggregate is 10 mm, and anything most of which passes 4.75 mm is fine aggregate. “6 mm” is a crusher trade name for small chips that sit across that boundary. It sells for block making, paver work and as a filler, but before it goes into structural concrete ask for its sieve analysis and let the engineer decide whether it is treated as coarse or fine aggregate.

At the other end, dams, thick rafts and other mass concrete use bigger stone. Table 8 of IS 383 sets four mass-concrete classes, each with 90 to 100 per cent passing the upper sieve and 0 to 10 per cent passing the lower one.

IS 456 also allows “plums”, stones larger than 160 mm, in plain concrete up to 20 per cent of the volume, where the engineer permits it and no plum sits closer than 150 mm to the surface.

How does a crusher plant make each size?

The crusher breaks the rock and the screen sorts it. A vibrating screen stacks several decks of mesh, the coarsest on top. Stone too big for the top deck goes back to the crusher. What passes the top deck but stays on the next one becomes the 40 mm product; what drops one deck further becomes 20 mm, then 10 mm, and whatever falls through the bottom deck is dust. Change the mesh and you change the products. Which crusher does which stage, and how the closed side setting moves the split, is explained in jaw crusher vs cone crusher vs VSI.

Size is only half of what IS 383 checks. The same standard caps the shape and strength of the stone:

• Combined flakiness and elongation index, the share of flat and long pieces added together, no more than 40 per cent.
• Aggregate impact value no more than 30 per cent for wearing surfaces such as roads, runways and pavements, and 45 per cent for other concrete.
• Los Angeles abrasion value no more than 30 per cent for wearing surfaces and 50 per cent for other concrete.

Flat, splintery chips are what push the first index up, and a cone or VSI stage makes more cubical stone, which is one reason plants add them. Road layers follow MoRTH, not IS 383, and their limits tighten toward the top layer; those are listed under road construction materials and their tests.

For a crusher owner the size split is also a money question, since each size sells at a different rate and some move slower than others. That side is covered in stone crusher business profit. The rest of the quarry side, from leases to royalty, sits in the mining guide.

Which machines handle aggregate on site?

At the crusher and the stockyard, a wheel loader moves the sized stone onto tippers. On a building site the size question returns at the mixer, because IS 456 wants coarse and fine aggregate batched separately and measured.

That is the job a self-loading concrete mixer is built for. Its front bucket scoops 20 mm, 10 mm and sand one after another, and across the 38 self-loading mixer models DesiMachines carries, 31 name an on-board weighing system in their specifications (as of Oct 2026). Bucket sizes run from 320 to 800 litres. The AJAX ARGO 4500 carries a 600 litre bucket and a pressure transducer or load cell, the Schwing Stetter SLM 4300 a 600 litre bucket with dual pressure sensors, and the Apollo Carmix 30 FX a 400 litre bucket with a load cell. Weighing each size as it goes in is how a site keeps a graded blend the same from the first batch to the last.

To compare drum sizes, weighing systems and dealer offers side by side, see the full range of concrete mixers.

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 clauses are quoted from IS 383:2016 (with Amendment 1, 2017) and IS 456:2000; your structural drawings and the engineer-in-charge take precedence over any general guidance here.