Concrete & Stone Calculator
Yards and bags for the pour, tons of stone for the base — both on this page, waste already included.
How the calculator works
Concrete is sold by volume. Ready-mix trucks deliver by the cubic yard, and bagged mix is labelled by the cubic feet one bag yields once mixed. So every estimate comes down to the same three steps:
- Find the volume in cubic feet. For a slab or footing that is length × width × thickness, all in feet (4 inches = 4 ÷ 12 = 0.333 ft). For a round column it is π × (diameter ÷ 2)² × height. For solid stairs each step is a block as wide as the stairs, as deep as the run, and one rise taller than the step below, so the total is width × run × rise × n(n+1) ÷ 2 for n steps.
- Add waste. Subgrade is never perfectly flat and some mix always stays in the wheelbarrow. 10% is the usual allowance; running short mid-pour is far more expensive than a little left over.
- Convert. Divide cubic feet by 27 for cubic yards. For bags, divide cubic feet by the yield of one bag and round up to a whole bag.
Worked example
A 10 ft × 10 ft patio, 4 in thick: 10 × 10 × 0.333 = 33.3 ft³. Add 10% → 36.7 ft³. Divide by 27 → 1.36 yd³, so order 1.5 yd³ from a truck, or buy 62 eighty-pound bags (36.7 ÷ 0.60 = 61.1, rounded up).
Bag yields we use
| Bag | Yield | Bags per yard | Covers at 4 in |
|---|---|---|---|
| 80 lb | 0.60 ft³ | 45 | 1.8 sq ft |
| 60 lb | 0.45 ft³ | 60 | 1.35 sq ft |
| 50 lb | 0.375 ft³ | 72 | 1.1 sq ft |
| 40 lb | 0.30 ft³ | 90 | 0.9 sq ft |
Sakrete and store-brand mixes publish nearly identical yields. Sand/topping mix (no gravel) yields more and is not for slabs.
Common questions
How many 80 lb bags of concrete make a yard?
45. A cubic yard is 27 ft³ and an 80 lb bag yields about 0.60 ft³, so 27 ÷ 0.60 = 45 bags — roughly 3,600 lb of mix to carry and mix by hand.
Should I order a truck or buy bags?
Under about one cubic yard, bags are practical. Above that, mixing 45-plus bags by hand gets slow and inconsistent, and most suppliers will deliver small loads (with a short-load fee). Enter prices in the options above to compare.
How thick should my slab be?
4 in for patios, sidewalks and shed floors; 5–6 in for driveways and anything a vehicle parks on; 6 in or more for workshop floors that take heavy equipment. Check local code for footings — depth is set by your frost line.
Why round up to a quarter yard?
Ready-mix plants batch in quarter-yard increments, so that is the smallest step you can actually order. We round your volume up to the next quarter so the number on screen is the number you say on the phone.
How much concrete do I need for stairs?
Three solid steps, 4 ft wide with a 7 in rise and 11 in run, come to about 0.40 yd³ with waste — around 18 eighty-pound bags. Pick the Stairs tab above and enter your own rise, run and width; add a landing depth if the top step is a platform.
Do I need gravel under my slab?
Almost always: 4 in of compacted crushed stone gives drainage and a stable base. Use the stone and gravel calculator to get the tonnage, or click the link under the slab inputs to carry your dimensions across.
How the stone calculator works
Bulk stone is sold by weight — the truck drives over a scale on the way out. Bagged stone is sold by volume. So the calculator works out volume first, then converts to tons with the density of the material you picked:
- Find the finished volume. Length × width × depth, all in feet (3 inches = 0.25 ft). For a circle it is π × (diameter ÷ 2)² × depth.
- Allow for compaction. Crusher run and stone dust shrink 15–20% when tamped; #57 stone about 10%; rounded river rock barely at all. If your depth is the finished, compacted depth, you need to buy that much more loose material.
- Add waste and convert. Add 10% for uneven ground, divide cubic feet by 27 for cubic yards, and multiply by tons per yard. We round up to the next quarter ton under 2 tons and the next half ton above, because that is how yards sell it.
Worked example
A 20 ft × 10 ft shed base, 3 in of #57 stone: 20 × 10 × 0.25 = 50 ft³. Compaction (10%) → 55.6 ft³. Waste (10%) → 61.1 ft³ = 2.26 yd³. At 1.40 tons per yard that is 3.17 tons, so order 3.5 tons, or buy 123 half-cubic-foot bags — which is why bulk wins above a ton.
Densities we use
| Material | Tons / yd³ | Compaction | Typical use |
|---|---|---|---|
| Crushed stone #57 (¾ in) | 1.40 | 10% | Drainage, slab base, driveways |
| Crusher run / dense grade | 1.50 | 20% | Compacted driveway and paver base |
| Pea gravel (⅜ in) | 1.35 | 5% | Paths, play areas, decorative beds |
| River rock (1–3 in) | 1.30 | 0% | Dry creek beds, decorative |
| Crushed limestone | 1.35 | 12% | Driveways, arenas, farm lanes |
| Stone dust / crusher fines | 1.60 | 20% | Paver bedding, compactable paths |
| Sand (masonry / paver) | 1.35 | 10% | Paver bedding, sandboxes, leveling |
Wet material weighs 10–15% more. If it rained on the pile, expect the scale ticket to read heavier than this estimate for the same volume.
Common stone & gravel questions
How much does a cubic yard of gravel weigh?
Loose and dry, most crushed stone and gravel weighs 1.3 to 1.5 US tons (2,600–3,000 lb) per cubic yard. Dense-grade crusher run and stone dust run heavier at 1.5–1.6 tons; river rock and pea gravel lighter at about 1.3–1.35.
How much area does a ton of gravel cover?
At 2 in deep, a ton of ¾ in crushed stone covers roughly 115 sq ft. At 3 in about 77 sq ft, and at 4 in about 58 sq ft. Enter your own area above and the calculator shows coverage next to the bag count.
What stone goes under a concrete slab?
Usually 4 in of compacted #57 crushed stone or crusher run. It drains, stops the slab wicking moisture and gives a uniform base. Once you have the stone, switch to the concrete calculator for the slab itself — the two tools pass dimensions back and forth.
Should I buy bags or bulk?
A cubic yard is 54 half-cubic-foot bags, so bags only make sense for very small jobs — a tree ring, a sandbox, topping up a path. Above about a ton most yards will deliver, and many sell a half-yard "scoop" you can collect in a pickup.
How deep should a gravel driveway be?
A new driveway on soil wants 6–8 in total: 4 in of crusher run base, compacted, then 2–3 in of #57 or pea gravel on top. Resurfacing an existing driveway needs only 2 in. Calculate each layer separately with its own material.