20mm gravel calculator

This calculator works in area mode: multiply the footprint you give it by the depth, apply the density of 20mm gravel, and convert the result into tonnes, cubic metres or a bulk bag count. That is the right shape of sum for a driveway, a path or a gravel garden bed, all of which are a flat area at a roughly constant depth. Measure the area in metres rather than estimating by eye, since even a small error in length or width gets multiplied twice over, once by width and once by depth, before it reaches the final tonnage, and that compounding is easy to underestimate on a larger area like a full driveway. A long tape or a measuring wheel is worth the extra few minutes over pacing out the distance, particularly on a drive or path that bends or narrows partway along its length.

Bulk bags are a fixed unit, typically somewhere around 800 to 900 kilograms depending on the supplier, so the calculator's tonnage figure almost never divides evenly into whole bags. Round up rather than down, since a part used bag sitting in the garden is a minor inconvenience while running short mid job means a second delivery charge for the shortfall. A loose tipped load from a bulk tipper does not have this problem, since the supplier can bring the exact tonnage you calculated, but it generally needs vehicle access right to the area being covered, which a driveway usually has and a back garden rarely does, so check access before assuming a loose tip is the cheaper option.

20mm and 10mm gravel are often chosen on looks as much as function, and it is worth deciding on that basis rather than defaulting to whichever one a supplier has in stock. The larger 20mm stone reads as a chunkier, more substantial material and tends to stay put better in an area that gets vehicle traffic or regular foot traffic, while the finer 10mm gravel calculator suits borders, pots and areas where a finer, more even texture matters more than load bearing. Neither locks together the way a crushed angular stone does under compaction, so a driveway built purely from decorative 20mm gravel without a proper sub base underneath will rut over time regardless of which size you pick, and that sub base is a separate material and depth from the decorative layer itself.

For a driveway specifically, 20mm gravel is usually the visible top dressing over a separate compacted sub base rather than the whole depth of the build, and skipping the sub base is the most common reason a new gravel driveway ruts within the first year. The gravel driveway calculator covers that full layered build, and the broader crushed stone calculator is there if the sub base itself is an angular crushed stone rather than the decorative 20mm layer this page is sized for. Pricing the two layers separately before ordering also makes it easier to see where the budget is actually going, since the sub base often makes up more of the total tonnage than the visible decorative layer on top of it.

Once you have a tonnage figure, it is worth checking it against pricing before you commit, since bulk bag and loose tip pricing from the same supplier can differ more than expected once delivery is factored in; the gravel cost calculator takes this page's output straight into a cost estimate. If the units on your supplier's quote do not match what this calculator gives you, this explainer on tonnes, cubic metres and kilograms covers the conversions, and this guide to gravel depth is worth a read if you are still unsure what depth to enter in the first place, particularly if the project combines a decorative layer with a sub base at a different depth underneath it. Comparing two or three local suppliers on both the tonnage figure and the delivery charge is usually worth the phone calls, since the stone itself tends to be priced similarly while delivery fees vary a good deal by distance and minimum order size.