Gravel calculator
Volume is the easy half. Gravel is sold by weight, so the number you actually order depends on how heavy your particular stone is.
Why density is a field here
Crushed stone, pea gravel and river rock all occupy space differently. Most landscape gravel falls between 95 and 105 pounds per cubic foot, which is why 100 is the default — but denser crushed material can run higher, and lightweight decorative stone lower. If your supplier publishes a figure for the product you are buying, use theirs.
Depth depends on the job. Two to three inches suits a decorative bed or a top dressing. A driveway wants four inches or more, usually over a compacted base layer of larger stone, and that base is a separate calculation at its own depth.
One thing this cannot account for: compaction. Gravel settles when it is driven on or plate-compacted, typically losing something like a fifth of its loose volume. For a driveway, order for the settled depth you want and expect to add a little later rather than ordering exactly and coming up short.
Questions
How deep for a driveway?
Four inches of surface gravel is a common minimum, laid over a compacted base of larger stone. Decorative beds and paths need only two to three.
What density should I enter?
Around 100 pounds per cubic foot covers most landscape gravel. Ask your supplier for the figure on your specific product if you are ordering a large quantity, since the difference compounds.
Do I need extra for settling?
Yes if it will be driven on or compacted — expect to lose roughly a fifth of the loose volume. Order for the finished depth you want rather than the loose depth.