How to measure for bark
Measure the area you want to cover. For a rectangular border or a straight path, take the length (A) and width (B), checking the width in a few places. For a winding path, measure along its centre line and use the average width: a rectangle of that length and width is close enough. Round beds and tree circles are circles, corner beds triangles, and beds that wrap round a lawn L-shapes. Use Add another area for each piece.
Then set the depth: the thickness of bark you want once it has been spread and has settled. Bark is sold by volume, so the calculator works in litres, and every 10 mm spread over one square metre takes 10 litres. If you measure in feet and inches, switch the units at the top of the bark calculator. UK suppliers still sell in litres, and that is how the answer comes out.
Recommended bark depths
A bark mulch only keeps weeds down and moisture in if it is thick enough. These are the depths from Melcourt, the RHS and Quality Garden Supplies. The buttons set the calculator to each one.
| Use | Layer depth | Apply |
|---|---|---|
| Bark mulchKeeps weeds down and moisture in. | 50–100 mm of bark mulch | |
| Wood chip mulchWood chip can go deeper than bark. | 80–120 mm of wood chip | |
| Woodland pathFinished depth after treading down. | 70 mm of wood chip |
The path depth is a finished depth, once the chips have been walked on and have settled, which is why the calculator adds an extra allowance on top. Bark under children’s play equipment is a safety surface, not a mulch: the depth it needs depends on the fall height, so follow the equipment manufacturer’s guidance rather than this table.
Bark mulch calculator for borders
Ornamental bark is the tidy, decorative mulch for beds and borders. Melcourt suggests a layer of 50–100 mm, and the Bark mulch button starts in the middle of that range, at the depth the RHS calls ideal for a mulch.
Dig out perennial weeds and water dry soil before you spread it, then keep the bark clear of plant stems and trunks. The same sums work for any mulch sold by the litre, so you can use this as a general mulch calculator: pick the nearest depth and change the bag size to match what you are buying.
Bark chippings, nuggets and wood chip
Bark chippings come in grades from fine mulch to large nuggets. The grade does not change how many litres you need for a given depth, so use the same calculation for any of them and choose the bag size your supplier sells.
Wood chip is chipped branches and timber rather than bark. The RHS suggests a deeper layer of 80–120 mm when it is used as a mulch, and fresh wood chip is best left on the surface rather than dug in. Choose Wood chip mulch and the calculator switches to wood chip and its bags.
Wood chip calculator for woodland paths
A chip path needs a firm, even layer that stays put underfoot. Melcourt recommends laying its walk chips to a finished depth of at least 70 mm and says they settle by 5–10% as they are trodden down. The Woodland path button uses that depth, and the extra allowance covers the settling.
Give the path an edge of timber boards or logs so the chips stay where they are put, and top it up as it wears. If you would rather have a firmer surface, see the gravel calculator.
Worked example: a wood chip woodland path
Here is the full calculation for a straight woodland path using the Woodland path preset and the suggested extra allowance. Every line comes from the same code that runs the calculator above.
- Area 10 m × 1 m = 10.00 m²
- Volume 10.00 m² × 0.07 m (70 mm) = 0.700 m³
- In litres, plus extra 0.700 m³ × 1,000 + 10% = 770 litres
- In bags 770 ÷ 40 litres = 19.3, rounded up = 20 bags
On the list:
Notice that the list is all in bags. The calculator only has a bag size for wood chip, because that is how the suppliers we checked sell it. If your supplier offers wood chip in bulk bags, compare by litres: divide the litres above by the volume of their bag and round up.
UK bark bag sizes
Bark and wood chip are sold by volume. Melcourt sells its bark in bags of 60 litres and in bulk bags of 600 litres for bigger jobs, and Quality Garden Supplies sells wood chip in bags of 40 litres. Bulk bags are delivered by lorry, so check there is somewhere firm to set them down.
| Product | Size | Good for |
|---|---|---|
| 40 litre bag | 40 litres | Bag of wood chip. |
| 60 litre bag | 60 litres | Large bag of compost or bark. |
| Bulk bag, 0.6 m³ | 600 litres | Bark bulk bag. |
Bark settles after it is spread and once it has been rained on. Melcourt allows 5–10% for this, and the calculator starts at the upper figure; you can change it with the slider.
Common mistakes when buying bark
- Spreading too thin. A thin layer lets light through and weeds come straight up. Keep to the depth in the table.
- Spreading over weeds. Bark won’t stop established perennial weeds. Dig them out first.
- Burying stems. Bark heaped against stems and trunks keeps them wet. Leave a small gap round each plant.
- Comparing bags by number. A bag of wood chip and a bag of bark are different sizes. Compare by litres.
- Using garden bark under play equipment. Play surfaces have their own grades and depths. Follow the equipment manufacturer’s guidance.
- Forgetting it settles. Loose bark sinks as it beds down. Leave the extra allowance on, especially on paths.
What else you'll need
- Compost or soil improver to dig in before you mulch a new bed: use the compost calculator.
- Gravel and weed membrane for a harder-wearing path: the gravel calculator covers both.
- Plants for the border: the plant spacing calculator works out how many you need.
- Edging in timber boards or logs to keep a chip path in place.
- A rake, a shovel and a wheelbarrow, plus a sheet to tip bulk bags onto.
Last checked 28 October 2026