Why are the results called estimates?

Because the density of bulk material changes with moisture and how compacted it is. A cubic yard of gravel can weigh anywhere from 1.25 to 1.5 tons depending on the stone and the weather. We use mid-range industry figures and add a 10% allowance; treat the output as "order about this much", not a guarantee.

Where do the density numbers come from?

From ASTM C29 bulk-density test data, ready-mix industry figures for concrete, published bag yields from Quikrete and Sakrete, and delivered-density tables from landscape suppliers, cross-checked against each other. The full list is below.

A cubic yard is 3 ft × 3 ft × 3 ft, which is 27 cubic feet. Every volume is calculated in cubic feet first (area in square feet × depth in feet) and then divided by 27 to get the cubic yards a supplier quotes.

Is my data sent anywhere?

No. Every calculation runs in your browser with JavaScript. The dimensions and prices you type are never sent to a server, never stored, and never logged. You can use the tool offline once the page has loaded.

How is the bag count worked out?

We divide the required volume in cubic feet by the published yield of one bag (about 0.6 cubic feet for an 80 lb concrete bag, 2 cubic feet for a bagged mulch or soil bag), then round up, and show a second figure that includes the waste allowance.

Why does the calculator suggest ordering 10% extra?

Loose material compacts under its own weight and under traffic, ground is never perfectly level, spreading wastes some at the edges, and a delivered ton is weighed with moisture that later dries off. Ten percent covers all of that for most jobs; driveways and structural fill sometimes use 15%.

Do you account for compaction?

Indirectly, through the waste allowance. If you need a specific compacted depth, such as a road base or decomposed-granite path, order for the loose depth, which is roughly a third more than the finished compacted volume, and the guidance on those pages explains the adjustment.

What if my area is not a rectangle, circle or triangle?

Break it into shapes you can measure, run each through the calculator, and add the results, or set the "number of areas" field if the shapes are identical. For a ring or border, the tool has a dedicated shape that subtracts the inner area for you.

How we calculate

Every estimate on Bulk Material Calculator is the same three steps, done in a fixed order so the arithmetic is auditable. This page sets out the formulas, the density figures we use, why the results are estimates rather than guarantees, and the standards and manufacturer data the numbers come from.

Step 1: area

The area of the surface you are covering, in square feet, with every dimension converted to feet first:

Rectangle or square: length × width
Circle: π × (diameter ÷ 2)²
Triangle: ½ × base × height
Ring or border: π × (outer radius² − inner radius²)

If you set the number of identical areas, the area is multiplied by that count before anything else.

Step 2: volume

Volume in cubic feet is area × depth, with the depth converted to feet (so 3 inches becomes 0.25). Cubic feet ÷ 27 gives cubic yards; cubic feet × 0.0283 gives cubic metres. The cubic-yard figure is the one most suppliers quote.

Step 3: weight, bags and cost

Weight in tons is cubic yards × the material's density in tons per cubic yard. Bag counts are volume in cubic feet ÷ the yield of one bag, rounded up. Cost is the quantity in your chosen unit (cubic yards, tons or bags) × the price you enter. Each of these is also shown with the waste allowance added.

The density figures

These are typical delivered, settled densities for each material in its normal sold state, dry unless noted. Real deliveries vary ±10–15% with moisture and compaction, which is the single biggest reason the results are estimates.

Typical densities for gravel and crushed stone
Material	lb / ft³	tons / yd³	Sold by	Typical use
Pea gravel (3/8″, rounded)	100–105	1.35	ton or yd³	Paths, patios, dog runs, drainage
#57 crushed stone (3/4″, washed)	100–105	1.35	ton	Drainage, slab sub-base, French drains
3/4″ minus / dense-grade	105–115	1.45	ton	Driveway base, paver base, road pack
Crushed concrete (RCA)	100–110	1.35	ton	Driveway base, structural fill (cheaper)
River rock (1–3″)	95–105	1.40	ton or yd³	Dry creek beds, borders, xeriscape
Decomposed granite	110–120	1.50	ton	Paths, patios, natural-look driveways
Road base / Class 5	110–120	1.50	ton	Compacted base under pavers, slabs, drives

Typical densities for soil products
Material	lb / ft³	tons / yd³	Sold by	Typical use
Screened topsoil (dry)	75–85	1.10	yd³ (some ton)	New lawns, bed top-up, levelling
Topsoil (moist)	95–110	1.40	yd³	As delivered after rain; weighs more
Fill dirt / structural fill	90–100	1.25	ton or yd³	Raising grade, backfill, berms
Compost	40–50	0.55	yd³ or bag	Bed amendment, lawn top-dressing
Garden / raised-bed mix	65–80	1.00	yd³ or bag	Filling raised beds (soil + compost blend)

Typical densities and coverage for mulch
Material	lb / ft³	tons / yd³	Sold by	Coverage per yd³
Shredded hardwood / bark	18–22	0.45	yd³ or 2 ft³ bag	~160 ft² at 2″, ~108 ft² at 3″
Wood chips (arborist)	15–20	0.40	yd³	~160 ft² at 2″
Rubber mulch (playground)	35–50	0.63	bag or pallet	~2 ft² per ft³ at 6″
Pine straw	n/a	n/a	bale	~40–50 ft² per bale
Compost mulch	40–50	0.55	yd³	~160 ft² at 2″

Ready-mix and bagged concrete yields
Product	Yield	Per cubic yard	Best for	Notes
Ready-mix (delivered)	1 yd³ per yd³	N/A	Slabs, driveways, footings > ½ yd³	Short-load fee under ~1 yd³
80 lb bag	~0.60 ft³	45 bags	Small pads, posts, repairs	~4,000 psi mixed
60 lb bag	~0.45 ft³	60 bags	Post setting, small footings	Common fence-post size
50 lb bag	~0.375 ft³	72 bags	Small repairs
40 lb bag	~0.30 ft³	90 bags	Patching, setting small posts
Cured concrete weight	N/A	~4,000 lb (2 tons)	N/A	145–150 lb/ft³

Common quantities at a glance

How much is a cubic yard?

Bulk material is sold by the cubic yard. These are the numbers behind that unit.

1 cubic yard: 27 cubic feet0.765 m³202 US gallons A cube 3 ft on every side. Almost everything loose (stone, soil, mulch, ready-mix) is quoted and delivered in these.
What 1 cubic yard covers: 324 ft² at 1″162 ft² at 2″108 ft² at 3″81 ft² at 4″ Depth is what drives the order. Double the depth and you halve the area one yard will cover.
1 ton of gravel covers: ~100 ft² at 2″~50 ft² at 4″ Gravel runs about 1.4 tons per cubic yard, so a ton is roughly ¾ of a yard. Useful when a supplier prices by the ton and you measured in yards. Gravel calculator
1 cubic yard of mulch: 13.5 bags of 2 ft³covers ~160 ft² at 2″ Bagged mulch costs far more per yard than bulk. Past about a yard, a delivered load is usually cheaper even with the delivery fee. Mulch calculator
Concrete for a 10×10 slab: 4″ ≈ 1.23 yd³6″ ≈ 1.85 yd³ A 100 ft² pad. Thickness matters more than area: going from 4″ to 6″ adds half a yard to the same slab. Slab calculator
Concrete bags per cubic yard: 45 bags (80 lb)60 bags (60 lb)72 bags (50 lb)90 bags (40 lb) Past about half a yard (some 23 of the 80 lb bags), ready-mix is cheaper per yard and far quicker to place. Every bag size

Converting between units

Mixing units is the mistake that costs the most. These three conversions cover nearly all of it.

Inches of depth to feet: 1″ = 0.083 ft2″ = 0.167 ft3″ = 0.25 ft4″ = 0.333 ft6″ = 0.5 ft Divide inches by 12 first. Multiplying square feet by a depth still written in inches is how an order comes out 12× too big.
Cubic feet to cubic yards: divide by 27 Length × width × depth, all in feet, gives cubic feet. Divide by 27 for the figure your supplier wants.
Cubic yards to tons: gravel × 1.4sand × 1.35topsoil × 1.1concrete × 2.0mulch × 0.5 Multiply by the density of that material. Divide instead to go from a quoted tonnage back to yards. Full density table

Before you order

What a delivery actually looks like, and how much to add on top of the calculated figure.

Tandem dump truck: 10–14 cubic yards≈15–20 tons One full load. Check the truck can reach the drop point and that you have somewhere to put a pile that size.
Recommended over-order: 10% typical15% for driveways Covers settling, compaction and spillage. Running short means a second delivery fee for a fraction of a load.

Every bag size, and what one bag covers at each depth, is on the bags per cubic yard reference page.

Why the results are estimates

Bulk material is not a manufactured product with a spec sheet. The same gravel pit sells stone that weighs differently in July and in November. Mulch settles by a fifth in its first season. Topsoil delivered the morning after rain can weigh a third more than the same soil in a dry week. We publish mid-range figures, show the density each result used, and default to ordering 10% extra so a normal variation does not stop your job.

Sources

Source	What it informs
ASTM C29 / C29M	Standard test method for bulk density (unit weight) of aggregate, the basis for the lb/ft³ figures.
ASTM D448 / #57, #8 stone gradations	Standard sizes of coarse aggregate, used for the stone descriptions.
ASTM C33	Concrete aggregate spec that defines the coarse "concrete sand" specified for paver bedding.
Manufacturer bag data (Quikrete, Sakrete)	Published yields for 40 / 50 / 60 / 80 lb pre-mix bags (0.30–0.60 ft³).
NRMCA / ready-mix industry figures	Fresh and cured concrete unit weight (~145–150 lb/ft³, ~4,000 lb per yd³).
USDA & extension-service guidance	Mulch and topsoil depths for lawns, beds and trees.
Landscape-supply density tables	Cross-checked delivered densities for mulch, soil, river rock and decomposed granite.

Figures are reviewed against these sources on publication and rechecked when a user reports a discrepancy. Last reviewed 2026-09-07. Spot an error? Email hello@bulkmaterialcalculator.com with the inputs you used and the number you expected.