Multiply length × width × thickness in feet by the rock’s solid density: a 4 × 2 ft granite slab 2 inches thick is 1.33 ft³ × 168 lb = about 224 pounds. Solid stone runs 145–185 lb per cubic foot depending on the rock type.
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Boulder weights use sphere volume with a 0.66 irregularity factor — real boulders are never perfect spheres.
Stone Weight Calculator Guide
This calculator answers a different question from the rest of the site: not “how much stone fills this hole” but “how heavy is this particular piece of rock.” Solid natural stone — a slab, a step tread, a hearthstone, a bench top — is weighed with the rock’s solid density, which runs 145–185 lb per cubic foot depending on the type. That’s 40–60% heavier than the bulk densities used for crushed material, because a solid piece has none of the air voids that fill a loose pile.
The formula for a slab is length × width × thickness (all in feet) × density. A 4 × 2 ft granite slab at 2 inches thick is 4 × 2 × 0.167 = 1.33 ft³, and at granite’s 168 lb/ft³ that’s about 224 lb. For irregular boulders the calculator switches to a sphere-based estimate with an industry irregularity factor — see the dedicated boulder tool for that shape.
How Much Does Each Rock Type Weigh?
| Rock type | lb per ft³ (solid) | lb per sq ft at 1 in | 2 × 2 ft slab, 2 in thick |
|---|---|---|---|
| Sandstone | 145 | 12.1 | 97 lb |
| Flagstone | 150 | 12.5 | 100 lb |
| Concrete | 150 | 12.5 | 100 lb |
| Limestone | 156 | 13.0 | 104 lb |
| Bluestone | 160 | 13.3 | 107 lb |
| Quartzite | 165 | 13.8 | 110 lb |
| Fieldstone | 165 | 13.8 | 110 lb |
| Granite | 168 | 14.0 | 112 lb |
| Marble | 170 | 14.2 | 113 lb |
| Slate | 172 | 14.3 | 115 lb |
| Basalt | 185 | 15.4 | 123 lb |
The middle column is the workhorse number: multiply lb-per-square-foot-per-inch by the thickness in inches and you can weigh any slab in your head. Granite at 1.25 inches (a common countertop thickness) is 14 × 1.25 = 17.5 lb per square foot — so a 25 sq ft counter run weighs about 440 lb before cutouts.
Handling Heavy Stone Without Regret
- Set hand-move limits before lifting. One person handles about 75 lb of awkward stone; two people, 150 lb over short distances. The table above shows how quickly modest slabs blow past both numbers.
- Machines start at 500 lb. Steps, large treads, and anything in the quarter-ton class want a ball cart, skid steer, or the supplier’s boom truck. Book placement at delivery — repositioning later costs more than doing it right once.
- Weight decides the substrate. A 300-lb hearthstone needs a framed floor checked by span tables; a heavy stone bench needs a compacted base pad, or it will settle unevenly within a season.
- Verify the type, not the look. Grey “granite” steps are sometimes dense basalt — a 10% weight surprise on every piece. Ask the quarry for the density on the ticket when the placement is equipment-critical.
For rounded landscape rocks, the boulder weight calculator applies the sphere-and-irregularity method to a measured diameter. And for patio stone specifically, the flagstone weight calculator works in per-square-foot terms that match how flagstone is sold.
Frequently Asked Questions
How much does solid stone weigh per cubic foot?
Between 145 and 185 lb for common landscape rock: sandstone around 145, flagstone 150, limestone 156, granite 168, and dense basalt up to 185. That is solid, void-free rock — crushed aggregate weighs far less per cubic foot because of air space.
Why is this different from a gravel calculator?
Gravel calculators use bulk density, which includes the air between loose stones — around 100–115 lb/ft³. A single solid piece has no voids, so the same cubic foot weighs 40–60% more. Using bulk density on a slab badly underestimates its weight.
How heavy is a stone step or treads-sized piece?
A typical 4 ft × 16 in × 6 in stone step is about 2.2 cubic feet, which is 370 lb in granite or 320 lb in sandstone. Anything in that class needs machine placement or at least three strong people with bars and rollers.
What weight can I safely move by hand?
One person can manage about 75 lb of awkward stone, two people about 150 lb over short distances. Above that, rent a ball cart or hand truck; above 500 lb, plan on a skid steer or delivery-truck placement.