The short answer
Normalweight concrete
1 cubic foot 140 – 150 lb
1 cubic yard 3,780 – 4,050 lb (about 2 tons)
Structural lightweight
1 cubic foot 90 – 115 lb
1 cubic yard 2,430 – 3,105 lb
Source: NRMCA CIP 36. A band, not a number.
Why a range and not a figure
Because that is how it is published. NRMCA put normalweight concrete at
140 to 150 pounds per cubic foot, and the spread is real — it moves with
the aggregate, the mix design, and how much of the mix water is still in
there. Almost every other page answering this question picks one end,
usually 150 or a rounded 4,000 a yard, and presents it as the
answer without saying it chose.
The difference between the ends is 270 pounds a cubic yard. On a
three-yard load that is 810 pounds — the difference between a trailer
being inside its rating and over it.
Which end to work to
The top, for anything that has to hold it. A trailer
rating, a floor, a formwork prop, a lifting point. Over-stating a weight
costs you a bigger truck than you needed. Under-stating it is how axles
and falsework fail, and those failures do not degrade gracefully.
The bottom of the range is only useful when being wrong is cheap — a
rough sense of whether two people can move something, say.
What common slabs weigh
Normalweight concrete, from this calculator. The range is NRMCA's published band; the concrete alone, with no reinforcement counted.
Fresh against cured
Fresh concrete is heavier than cured concrete, because it is still
carrying all its mix water and some of that leaves. The published range
is for concrete in place. Weigh a delivery by the fresh figure and a
finished structure by the cured one — and note that for most small jobs
the difference sits inside the band above, which is one more reason a
band is the honest form of this answer.
Reinforcement
Steel is roughly three and a half times as dense as concrete, so rebar
adds weight twice: its own, less the concrete it displaces. How much
steel is in a given slab is a design decision rather than a property of
concrete, so this calculator asks for it rather than guessing. Leave the
field blank and you get the concrete alone, which is what the ticket
says.
Why anyone needs this
- Hauling. Half a cubic yard is over 2,000 lb — already past what a half-ton pickup should carry, before the truck.
- Formwork. Fresh concrete is a liquid, and its weight is the pressure trying to push your forms apart.
- Existing structures. A topping slab on a balcony or over a basement is a structural question. This is the first half of the answer; the second half is an engineer.
The rest of the job
To get the volume in the first place, the
slab calculator handles
rectangles and L-shapes and the
bags calculator converts between
volume and bags either way. For a curb or a footing the
curb calculator works from the
cross-section, and the
block fill calculator
covers concrete going into a block wall. When you are deciding how it
arrives, the guide to
bags or ready-mix is
largely a conversation about weight.
Common questions
How much does a cubic foot of concrete weigh?
Between 140 and 150 pounds for normalweight concrete. That is a range rather than a single figure because that is how NRMCA publish it in CIP 36 — the density moves with the aggregate, the mix and how much water is still in it. Structural lightweight concrete is 90 to 115 pounds a cubic foot. If you need one number to work to, use the top of the range: over-stating a weight costs you a bigger truck, and under-stating it is how axles fail.
How much does a cubic yard of concrete weigh?
3,780 to 4,050 pounds — call it two tons. A cubic yard is 27 cubic feet, so it is simply the per-foot figure multiplied by 27. In structural lightweight it drops to 2,430–3,105 pounds, which is most of the reason lightweight exists.
Why does every other site give one number?
Because one number is easier to write, and 4,000 pounds a yard is close enough to sound right. The published figure is a band — NRMCA put normalweight concrete at 140 to 150 pounds per cubic foot — and the difference between the ends of it is 270 pounds a yard, which is a real amount of weight on a trailer. This calculator reports the band and tells you which end to work to, rather than picking one for you and not saying so.
Is that fresh concrete or cured?
The published range is for concrete in place. Fresh concrete is heavier — it is still carrying all its mix water, and some of that leaves as it cures and dries. So weigh a delivery by the fresh figure and a finished structure by the cured one. For most practical purposes on a small job the difference sits inside the range above, which is another reason to work with a band rather than a point.
Does rebar change the weight?
Yes, twice over: steel is about three and a half times as dense as concrete, so reinforcement adds its own weight and displaces concrete that weighed less. But how much steel is in a slab is a design decision, not a property of concrete, and this calculator does not know it. So reinforcement is an optional field where you enter the weight of steel — it will not estimate a reinforcement ratio for you, because any figure it invented would be someone else's slab.
Why does it matter?
Three reasons, and all of them are about something holding the load. Hauling: a half-yard in a half-ton pickup is already over a thousand pounds of concrete before the truck. Formwork and falsework: fresh concrete is a liquid and its weight is what pushes forms apart. And existing structures: adding a topping slab to a balcony or a garage floor above a basement is a structural question, and the weight is the first half of it. This is the number, not the permission — the second half is an engineer.
What about bagged mix?
Bagged concrete mix gets a single figure rather than a range, because a manufacturer publishes one for their own product: QUIKRETE state 140 pounds per cubic foot by ASTM C138. That is the mixed density, not the weight of the dry bag. Ready-mix off a truck is denser — use normalweight for a delivery.
Sources
- Concrete mix density
- 140 lb/ft3
- 80 lb bag yield
- 0.6 ft³
- 60 lb bag yield
- 0.45 ft³
- 50 lb bag yield
- 0.375 ft³
- 40 lb bag yield
- 0.3 ft³
- 90 lb bag yield
- 0.675 ft³
- 30 kg bag yield
- 0.49440533379999996 ft³
- 20 kg bag yield
- 0.35314666699999997 ft³
- Default waste allowance
- 10%
- QUIKRETE Concrete Mix No. 1101 data sheet — published yields of 0.30, 0.375, 0.45, 0.60 and 0.675 ft3 for the 40, 50, 60, 80 and 90 lb bags, the 90 lb noted as regional availability
- QUIKRETE Concrete Mix No. 1101 data sheet — unit weight approximately 140 lb/ft3 per ASTM C138
- Sakrete Concrete Mix product data sheet, King Packaged Materials / Sika Canada — a 30 kg (66 lb) bag yields approximately 0.014 m3 (1/2 ft3)
- Blue Circle Multi-Purpose Concrete technical information, Tarmac — one 20 kg bag typically produces around 0.01 m3 of fresh concrete, supplied throughout the United Kingdom in 20 kg bags
- NRMCA Concrete in Practice CIP 36, Structural Lightweight Concrete — "Structural lightweight concrete has an in-place density (unit weight) on the order of 90 to 115 lb/ft3 (1440 to 1840 kg/m3) compared to normalweight concrete with a density in the range of 140 to 150 lb/ft3 (2240 to 2400 kg/m3)."
Bag yield is approximate and varies with aggregate and water content. Density 140 lb/ft3 is the ASTM C138 unit weight of mixed bagged concrete, about 3,780 lb/yd3, and is what every calculation here uses. Ready-mix delivered by truck is denser, about 150 lb/ft3 or 4,050 lb/yd3; that figure is stored separately as readyMixDensity and appears only where a page discusses ordering ready-mix. The two are not interchangeable. The 90 lb bag is regionally stocked rather than nationally, so it is flagged and listed last. Bag sizes are per market: the 40 to 90 lb bags are what North American merchants stock, and the 20 and 30 kg bags are what the UK, Canadian and Australian ones do. Switching the calculator to metric switches the shopping list with it, because a metric answer priced in pounds of product is not an answer anyone can buy. The 150 lb/ft3 ready-mix figure was carried for a long time as a point value with nothing behind it. NRMCA CIP 36 publishes it as the TOP of a range — normalweight concrete is 140 to 150 lb/ft3, and structural lightweight is 90 to 115 — so densityRanges now holds both and the weight calculator reports a span rather than a single number it cannot justify. Where one figure has to be picked, the top of the range is the safe end: over-stating a weight risks specifying too much truck, and under-stating it risks overloading one.
Unit conversions are exact by definition and need no source.
How we choose and cite these figures
