How Much Does a Yard of Slag Weigh? Chart by Slag Type

How much does a yard of slag weigh? It depends almost entirely on which slag you are buying. Air-cooled blast furnace slag, the porous gray stone from iron making, typically weighs about 1,900 to 2,300 pounds per cubic yard, or roughly 0.95 to 1.15 tons. Steel slag from steelmaking furnaces is much denser, about 2,700 to 3,240 pounds per cubic yard, or 1.35 to 1.6 tons. This guide puts every common slag type in one chart, shows how to turn yards into tons and back, and covers what to ask before a load shows up.

The short answer

Air-cooled blast furnace slag: about 0.95 to 1.15 tons per cubic yard (70 to 85 pounds per cubic foot compacted).
Steel slag: about 1.35 to 1.6 tons per cubic yard (100 to 120 pounds per cubic foot).
Expanded or pelletized slag: lighter still, roughly 0.7 to 0.9 tons per cubic yard.
Crushed quarry stone usually lands in between, so steel slag is heavier than gravel and blast furnace slag is usually lighter.
Use the supplier’s number when you have it. Slag varies by plant and by batch, and the scale ticket is what you pay for.

Slag weight per cubic yard by type

The figures below come from the Federal Highway Administration’s guidelines on byproduct materials in pavement construction (FHWA-RD-97-148), converted to a cubic yard (27 cubic feet) and to short tons of 2,000 pounds. The yards-per-ton column is simply the reverse.

Expanded (foamed) blast furnace slag: 50 to 65 lb/ft³, so about 1,350 to 1,755 lb per yard, 0.68 to 0.88 tons per yard, or 1.14 to 1.48 yards per ton.
Pelletized blast furnace slag: about 52 lb/ft³, so about 1,400 lb per yard, 0.70 tons per yard, or about 1.4 yards per ton.
Air-cooled blast furnace slag, typical: 70 to 85 lb/ft³, so about 1,890 to 2,295 lb per yard, 0.95 to 1.15 tons per yard, or 0.87 to 1.06 yards per ton.
Air-cooled blast furnace slag, high-iron batches: FHWA notes some recent material has tested as high as 120 lb/ft³, which is about 1.6 tons per yard.
Steel slag, from basic oxygen and electric arc furnaces: 100 to 120 lb/ft³, so about 2,700 to 3,240 lb per yard, 1.35 to 1.62 tons per yard, or 0.62 to 0.74 yards per ton.

For comparison, an FHWA report on blast furnace slag in concrete gives a typical range of 75 to 110 lb/ft³ for normal-weight aggregate, which works out to about 1.0 to 1.5 tons per cubic yard. Our own crushed stone weight guide and gravel weight per yard chart cover those products in more detail.

Metric version: air-cooled blast furnace slag is about 1,120 to 1,360 kg per cubic meter and steel slag about 1,600 to 1,920 kg per cubic meter.

Why steel slag weighs so much more

The two main kinds of slag form in different furnaces and end up with very different rock.

Blast furnace slag is the molten layer skimmed off when iron ore is turned into iron. Poured into beds and left to cool slowly in the air, it hardens into a crystalline stone full of small pores. FHWA lists its specific gravity at about 2.0 to 2.5, a bit below most quarried rock, and the pores make a yard of it lighter still.
Steel slag comes from refining iron and scrap into steel. It carries a lot of iron oxide, and FHWA puts its specific gravity at about 3.2 to 3.6. Each piece is simply heavier than a piece of limestone or granite the same size.
Expanded and pelletized slag are blast furnace slag treated with controlled amounts of water, or water and air, while molten, which leaves them puffed up and porous. They are made to be light and are used mainly as lightweight aggregate and in cement making, not as driveway stone.

Compacted, loose and wet weight

The unit weights in the chart are compacted values measured in a test container. Three things move the real number on your job:

Loose versus compacted. Slag dumped from a truck has more air between pieces than slag that has been rolled, so a loose yard weighs somewhat less than the chart and a rolled yard can weigh a bit more.
Gradation. A dense-graded slag with fines packs tighter than a clean, single-size stone, so it weighs more per yard. FHWA notes that compacted density shifts with size and grading.
Moisture. Air-cooled blast furnace slag can absorb up to about 6 percent water and steel slag up to about 3 percent, on top of any surface water from rain, and you pay for that water by the ton.

How many yards are in a ton of slag?

Divide 2,000 by the pounds per cubic yard. With typical figures:

Air-cooled blast furnace slag at 1.05 tons per yard: about 0.95 cubic yards per ton.
Steel slag at 1.5 tons per yard: about 0.67 cubic yards per ton.
Expanded slag at 0.8 tons per yard: about 1.25 cubic yards per ton.

So a 10-ton order is roughly 9.5 yards of blast furnace slag but only about 6.7 yards of steel slag, a big difference in how much ground it covers.

How many tons of slag do you need?

Cubic feet = length × width × depth, all in feet. Four inches is 0.33 feet.
Cubic yards = cubic feet ÷ 27.
Tons = cubic yards × the tons-per-yard figure for your slag.
Add about 10 percent for compaction, edges and uneven ground.

Example: a 12 × 50 foot driveway topped with 4 inches of slag is 600 × 0.33 = 200 cubic feet, or about 7.4 cubic yards. At 1.05 tons per yard for blast furnace slag that is about 7.8 tons, or roughly 8.6 tons with the extra. At 1.5 tons per yard for steel slag it is about 11.1 tons, or roughly 12.2 tons with the extra.

Turned into coverage, one ton spread 4 inches deep covers about 77 square feet of blast furnace slag at 1.05 tons per yard, but only about 54 square feet of steel slag at 1.5 tons per yard. The crushed stone calculator has a custom density setting, so you can enter your supplier’s tons-per-yard figure and skip the hand math.

Why the weight matters for delivery

Trucks are limited by weight as well as by bed size. A heavy product like steel slag can hit a truck’s legal weight before the bed is full, so you get fewer yards per load. If a truck can carry 15 tons, that is about 10 yards of steel slag at 1.5 tons per yard, but closer to 14 yards of blast furnace slag at 1.05, as long as the bed has room. See how many tons fit in a dump truck for typical truck sizes, and do not try to haul a full yard of steel slag in a half-ton pickup.

What about slag sand?

Granulated blast furnace slag, sometimes sold as slag sand, is molten slag quenched in water so it shatters into glassy, sand-size grains. Its best-known use is in cement and concrete, where it is ground into a fine powder. Its weight per yard depends on how it was processed, so get the figure from the seller rather than borrowing a number for regular sand.

Check these before the truck is booked

Which furnace did it come from? Steel slag versus blast furnace slag can change your tonnage by half again.
What does a yard weigh, in tons? Ask for the number they use for that exact product and size.
How long has steel slag been aged? Steel slag can contain free lime and magnesia that swell when they take on water. FHWA advises stockpiling it outdoors for several months, and up to 18 months in some cases, before use, and says it is not suitable as compacted fill under concrete slabs.
Is it near pipes or water? FHWA notes runoff from steel slag can reach a pH above 11, enough to corrode aluminum or galvanized pipe it touches.

For the pros, cons and build steps of using slag on a drive, read our slag driveway guide.

Questions people ask

How much does a cubic yard of slag weigh in pounds?

Air-cooled blast furnace slag typically weighs about 1,900 to 2,300 pounds per cubic yard, steel slag about 2,700 to 3,240 pounds, and expanded or pelletized slag roughly 1,350 to 1,750 pounds.

How many yards is a ton of slag?

About 0.87 to 1.06 cubic yards of air-cooled blast furnace slag, or about 0.62 to 0.74 cubic yards of steel slag. Divide 2,000 by the pounds per cubic yard for your product.

Is slag heavier than gravel?

Steel slag is usually heavier than crushed stone or gravel because it carries a lot of iron. Air-cooled blast furnace slag is porous and usually weighs the same or less than quarried stone.

How many tons of slag do I need for a driveway?

Multiply length by width by depth in feet, divide by 27 for cubic yards, then multiply by your slag's tons per yard. A 12 by 50 foot drive at 4 inches is about 7.4 yards, roughly 7.8 tons of blast furnace slag or 11.1 tons of steel slag before extra.

Does wet slag weigh more?

Yes. Federal Highway Administration data show air-cooled blast furnace slag can absorb up to about 6 percent water and steel slag up to about 3 percent, plus any surface water, and that water is weighed on the ticket.

What is slag sand?

Slag sand usually means granulated blast furnace slag, molten slag quenched in water into glassy sand-size grains. Its weight depends on processing, so ask the seller for a tons-per-yard figure.

Related guides

Open the crushed stone calculator →

As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.