Rock Calculator
Rock calculator works out Area covered and Depth from Material, Density from your supplier and What you are starting from. The default figures on this page give volume of 1.8617 yd3; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
5 steps
- Area = pi/4 x ((20 ft)^2 - (12 ft)^2) = 201.062 sq ft
- Depth = 3 in = 0.25 ft
- Volume = 201.062 x 0.25 = 50.2655 cu ft = 1.8617 cu yd
- Density = 100 lb/ft3 (EPA table: Stone, crushed - 1 cubic foot - 100 lb (FEECO))
- Weight = 50.2655 x 100 = 5026.5 lb = 2.513 US short tons
Figures from bulk material densities, checked 31 August 2026. Its 9 worked examples are re-run on every release, last on 15 September 2026. What changed · how reference data is kept current
Sources and references
4 sources
Keep this result
Save it, change one figure, then compare the two
The calculation stays free. Save this scenario, adjust one assumption, save that too, and put them side by side to see exactly what the change costs you. A free account keeps 5 scenarios and 2 comparisons; Personal makes both unlimited and adds exports and private links. Nothing is saved unless you press Save.
What the rock calculator calculates
Converts a covered area and spread depth - or a known tonnage, or a measured stockpile - into the volume of gravel, sand, topsoil, mulch, compost or decorative stone required, in cubic feet, cubic yards, cubic metres, bags, tons and tonnes, with a soil-blend split and cost by the yard, the ton or the bag.
How to use this rock calculator
Enter Material, Density from your supplier, What you are starting from and Shape of the area. Area covered updates as you type. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Area covered, Depth and Volume.
The method follows U.S. EPA, Standard Volume-to-Weight Conversion Factors (loose bulk densities for gravel, sand, stone, soil, wood chips and compost), ASTM C29/C29M, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate, NIST Special Publication 811, Guide for the Use of the International System of Units (exact ft-to-m and lb-to-kg conversions) and Interlocking Concrete Pavement Institute, Tech Spec 2: Construction of Interlocking Concrete Pavements (1 in / 25 mm screeded bedding sand course).
What you can compare
Change one input at a time to see how it affects Area covered, Depth and Volume. The inputs you can vary are Material, Density from your supplier, What you are starting from, Shape of the area, Length and Width.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate how much rock I will need?
Converts a covered area and spread depth - or a known tonnage, or a measured stockpile - into the volume of gravel, sand, topsoil, mulch, compost or decorative stone required, in cubic feet, cubic yards, cubic metres. Open “How this is worked out” beside the result to see each step for your own figures.
How much will 1 ton of rock cover?
On the figures this page opens with — length 20, width 10, depth of the layer 4 and extra for compaction, settlement and spillage 0% — the volume is 1.8617 yd3. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
How much does 1 yard of 57 stone cover?
It needs Material, Density from your supplier, What you are starting from, Shape of the area, Length and Width. Nothing else is required, and the figures stay in your browser.
How much does 30 lbs of rock cover?
The result gives Area covered, Depth, Volume, Order this much (rounded up to the half yard), Bulk density used and Weight, each labelled with its unit so the figure can be read on its own.
What information do I need for the rock calculator?
You need Material, Density from your supplier, What you are starting from, Shape of the area, Length, Width, Diameter (outer, for a ring) and Inner diameter of the ring. The page opens with default figures that give volume of 1.8617 yd3, so you can see the scale before entering your own.
What does this rock calculator show?
It shows Area covered, Depth, Volume, Order this much (rounded up to the half yard), Bulk density used, Weight, Bags needed and Order this much (rounded up to the half ton), with the working and any warnings for your entries.