[stonecalc id=”stone-weight”]
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.
[stonecalc_faq id=”stone-weight”]