Area (or enter your total area as the length and leave width at 1)
Depth
| Volume | Amount |
|---|
Buying it (density and bulk bag size are typical figures - edit if your supplier quotes different)
| Weight | 0.00 t |
| Bulk bags | 0 |
| 25L bags | 0 |
How this calculator works
Volume is length × width × depth, with the depth converted from millimetres to metres before multiplying. If you already know your total area rather than two dimensions, enter it as the length and leave width at 1. A waste and settlement allowance is added on top: topsoil compacts once it's spread, watered and walked on, so the loose volume you buy needs to be somewhat more than the finished depth you want, and a 5 to 10% allowance covers that plus the usual spillage.
How deep for a new lawn?
The right depth comes down to what's underneath. Grass roots spread sideways as much as down, so a shallow layer over poor ground gives them nowhere to go once the top few centimetres dry out in summer - that's why 150mm is the safer default for genuinely bare or stripped ground. If the existing soil is already reasonably loose and just needs enriching or levelling before turf or seed goes down, 100mm is usually enough, since the roots can carry on into what's already there. Raised beds and general levelling jobs use their own presets above because they're not root-depth decisions at all - a raised bed depth is set by what you're growing, and a levelling job by how uneven the ground is.
Tonnes versus cubic metres
Topsoil is bought by weight (tonnes) or volume (cubic metres, bulk bags, litres), and the two convert into each other via a bulk density figure - tonnes per cubic metre - that varies mainly with moisture: wet topsoil is heavier than the same soil dry. This calculator defaults to 1.5 t/m3, the middle of the 1.2 to 1.7 t/m3 range typically quoted for screened topsoil; use your supplier's own figure if they state one.
Bulk bag coverage
A bulk (jumbo) bag of topsoil typically holds around 0.7 m3, weighing roughly 850kg - stated here as two separate supplier-average figures rather than an exact conversion of each other, since bulk bags are rarely filled level to the top and settle differently depending on moisture. The calculator uses the 0.7 m3 figure to work out bag count directly from volume; edit it if your supplier's bags are a different size. For smaller top-ups, 25L poly bags are the usual retail size and are shown alongside the bulk bag count.
Topsoil for turf
Laying new turf is one of the most common reasons to buy topsoil, and the turf calculator covers both turf roll counts and a topsoil top-up in one place if that's your job - useful if you also need to know how many rolls to order. Use this page instead when you want the fuller set of presets (raised beds, general levelling) or need cubic metres and 25L bag counts specifically.
What this calculator does not check
This tool covers topsoil quantity only, not ground condition. A boggy patch that stays wet for days after rain has a drainage problem that piling on more soil won't solve - that needs sorting first. It also doesn't judge screening grade (finer, stone-free soil matters more for seeding than for turfing, where the turf itself covers small imperfections), or whether old weeds and roots need clearing before you spread anything on top.
Related tools
Buying gravel, sand or hardcore instead, or a mix of materials for a bigger job? The aggregate calculator covers those with the same area-and-depth approach. For a gravel-and-soil border or bed, the gravel calculator adds decorative depth presets and membrane guidance. Laying turf on top of your new topsoil? See the turf calculator for roll counts, or read the topsoil for turf guide for fuller depth, tonnes and bulk-bag guidance.
FAQ: how much topsoil do I need
How much topsoil do I need for a new lawn? For a 5m × 3m area (15 m2) at the new-lawn preset depth of 150mm, the raw volume is 15 × 0.15 = 2.25 m3. Adding the default 10% waste allowance takes that to 2.25 × 1.1 = 2.475 m3, shown rounded as 2.48 m3. At the default 1.5 t/m3 density that's 2.475 × 1.5 = 3.71 tonnes, or 4 bulk bags (2.475 ÷ 0.7 = 3.5, rounded up since a part-bag still means buying a whole one), or 99 x 25L bags (2.475 m3 = 2,475 litres ÷ 25).
How much topsoil do I need per square metre? At 150mm depth, each square metre needs 0.15 m3 before waste allowance, which is roughly 0.225 tonnes at the default density. Multiply by your area and add your waste allowance, or just enter the area above.
Is this the same as the aggregate calculator? The aggregate calculator also has a topsoil option and covers gravel, sand and hardcore too if you're buying more than one material for the same job. This page adds job-specific depth presets and a 25L bag count, which the aggregate calculator doesn't show.