What Is the Rock Weight Calculator?
This tool estimates how much a rock or boulder weighs based on its size and the type of stone. Knowing the weight matters when you are moving landscape boulders, loading a truck, sizing rigging and lifting gear, or buying stone by the ton. Because you rarely have a scale big enough for a boulder, the most practical method is to estimate its volume and multiply by the density of the rock.
How to Use It
Pick a shape. For an irregular boulder, treat it as a rectangular block using its longest length, width, and height — this slightly over-estimates, which is safe for lifting. For a rounded boulder choose the spherical option and enter the diameter. Then select the rock type, which sets the density. The calculator returns the weight in pounds, US tons, and kilograms, along with the computed volume.
The Formula
Weight is volume times density:
$$W = V \times \rho$$
where \(W\) = weight, \(V\) = volume in cubic feet, and \(\rho\) = density in pounds per cubic foot. A rectangular block has \(V = L \times W \times H\); a sphere has $$V = \tfrac{4}{3}\pi\left(\tfrac{d}{2}\right)^{3}.$$ Typical densities: granite ≈ 165, basalt ≈ 170, limestone ≈ 150 lb/ft³.
Worked Example
A granite boulder roughly \(2 \times 2 \times 2\) ft. Volume is $$V = 2 \times 2 \times 2 = 8\,\text{ft}^3.$$ With granite at \(165\) lb/ft³: $$W = 8 \times 165 = 1320\,\text{lb} \approx 0.66\,\text{US tons}.$$
FAQ
How accurate is this? It is an estimate. Real rocks are irregular and porous, so densities vary by ±10%. Use the block method for a conservative (heavier) figure.
Which density should I pick? Match the rock type if you know it; otherwise granite (165 lb/ft³) is a reasonable default for hard landscape stone.
What is a US ton here? A short ton equal to 2,000 pounds.
