Bark Mulch Calculator

Bark Mulch Calculator: Litres and Bags for Your Beds

Bark is the finishing layer that makes a bed look deliberate: it hides bare soil, holds moisture through dry spells and keeps most weeds from ever getting started. In the UK it is sold by the litre — in 50, 60, 70 and 100 litre bags at the garden centre, or by the bulk bag from a merchant — so the useful question is not how many cubic yards you need but how many litres, and how many bags that makes. If you have been reading US advice in cubic yards and cubic feet, our Mulch Calculator covers the same job in imperial units. This page is the UK version: metres, centimetres and litres throughout. Measure your bed, choose a depth, and the calculator gives you the volume, the bag count for the size you actually buy, and the bulk-bag equivalent for bigger jobs.

Quick answer

For a 20 m² bed at the standard 5 cm depth, you need 1,000 litres of bark — exactly 1.00 m³. That is 20 bags of 50 L, or 2 bulk bags. Go deeper, to 7.5 cm, and the same bed needs 1,500 litres: 30 bags of 50 L, or 3 bulk bags. The maths is only ever area × depth — every square metre at 5 cm deep takes 50 litres — but the rounding into whole bags is where orders go wrong, and the calculator below does that rounding for you.

How deep should bark be?

Depth is the decision that makes bark work or makes it a waste of money. 5 cm is the minimum for real weed suppression: at that depth the layer blocks the light that weed seeds need to germinate, and it is thick enough to slow the moisture leaving the soil underneath. 7.5 cm is better where you want the full effect — it holds more moisture through a dry summer, it looks richer and more deliberate, and because there is more of it, it lasts longer before it thins out. Below 5 cm, be honest about what you are buying: a 2–3 cm layer is decoration only. It colours the soil for a few months, but weeds grow straight through it and it does nothing for moisture. If the budget is tight, mulch fewer beds at 5 cm rather than every bed at 2 cm. And spread it evenly: a bed that is 8 cm in the middle and 2 cm at the edges behaves like the 2 cm bed wherever the weeds find the thin spots.

Coverage at a glance

The working is always the same: area in square metres × depth in centimetres × 10 gives you litres, because one square metre covered one centimetre deep is ten litres of bark. From that, the coverage figures worth remembering:

Amount of bark	Covers at 5 cm deep	Covers at 7.5 cm deep
One 50 L bag	1 m²	about 0.7 m²
One bulk bag (about 700 L)	14 m²	about 9 m²
1 m³ of bark	20 m²	about 13 m²

So 1 m³ of bark covers 20 m² at 5 cm, or about 13 m² at 7.5 cm — and one 50 L bag covers 1 m² at 5 cm, which makes garden-centre maths easy: pace out the bed in square metres and that is roughly your bag count at the standard depth. Bulk bags win on price per litre once a job passes about ten bags, and one delivery beats ten trips with a boot full of split plastic.

Types of bark

Three sorts cover most UK gardens, and they are not interchangeable:

• Composted bark: fine, dark and already part-rotted, so it blends into the soil quickly and improves it as it goes. The friendliest choice for planted beds, and the one that looks most like a finished garden — but it breaks down fastest, so it needs its top-up.
• Bark nuggets and chippings: the chunky grade. The bigger pieces are slower to break down, stay put better on slopes, and shrug off foot traffic, which is why they are the standard choice under play equipment and along informal paths.
• Pine bark: leans acidic as it breaks down, which suits acid-loving plants — rhododendrons, azaleas, camellias, heathers and blueberries. Use it around those and keep the neutral grades for everything else.

Whichever you choose, bark is a living layer, not a permanent one: it rots down into the soil it is protecting, which is good for the soil and means the layer gets thinner every year. Top up a thin layer each spring — typically a bag or two spread over the thinnest patches — and the bed stays covered without ever needing a full re-mulch.

What to calculate next

• Mulch Calculator — the US version of this page, in cubic yards, cubic feet and bags.
• Soil Calculator — if the bed itself needs raising or filling before the bark goes on.
• Sod Calculator — for the lawn side of the same garden project.

Frequently asked questions

Estimates only — bark settles and breaks down; a small top-up each year keeps beds covered.