Wood Chip and Bark Calculator

Key Takeaways

• Bark needed for a bed is the area in m² multiplied by the depth in mm, which gives the litres, plus 15% for settling. A 10m² border at 75mm takes 750L, or about 860L with the allowance.
• Bark and wood chip on beds works at 50 to 75mm to stop weeds and 75 to 100mm to hold moisture. A wood chip path needs 50 to 70mm and a chicken run 100mm. Anything over 100mm keeps rain off the soil.
• A 1,000L bulk bag of bark covers about 13m² at 75mm, 10m² at 100mm and 40m² as a 25mm top-up. Bag names mean different volumes between suppliers, so the litres on the listing are the figures to compare.
• Bark and wood chip orders need about 15% extra, because both settle once laid and walked on. A top-up on an existing layer needs about 25mm, once the old bark is raked through to show what is left.
• Bark and wood chip sold by the tonne converts to litres by weight. Bark weighs 250 to 350kg per m³ and spruce chip 206 to 320kg per m³, dry to wet, so a tonne of wood chip is about 3,100 to 4,900L.

I lost count of how many times I turned up to a job and found the client had ordered a bulk bag too many, or worse, a bag too few. One job comes to mind, where a customer had insisted on ordering the play bark for their kids' ninth birthday party present. Disaster! Unfortunately, they under-ordered the amount needed for safety for a play area, by two bags! Due to national stock levels for the deluxe pine play nuggets, there was none available. The entire party arrived to a play gym that was dangerously thin on bark, which stressed everyone involved and put a big damper on the party for all the kids, not to mention the added costs! They had to wait four weeks for a second delivery - if only they had a good calculator.

So, all you need to do is just measure up and pop the numbers in. Start calculating by picking a depth by the job type button, add any extra allowance and choose the product. Our calculator gives you two answers: the cheapest order based on Outdoor Aggregates shop prices, as well as the closest fit with the least left over. And if the calculator says you need more than about 8,000L, you are looking at a lorry load rather than a bag order. Call us and we will price it loose at a far better price.

Why Does the Cheapest Bark Order Leave Bark Spare?

The cheapest bark order is worked out from our live shop prices, and a large pack can cost less than several small bags.

Bigger packs carry a lower price per litre. One 30 x 60L pack of Border Bark (1,800L) costs £197, which is £0.11 a litre. Two 10 x 60L packs (1,200L) cost £234, which is £0.20 a litre. The bigger pack gives you 600L more for less money.

That is why the calculator shows two answers. The cheapest option saves money, and the spare bark keeps happily for next spring's top-up, bagged and out of the rain. The closest fit leaves the least left over, which matters if you have nowhere to store the rest. Tap the box you want and add it to your basket.

How Deep Should Bark or Wood Chip Be?

The depth of bark or wood chip depends on the job: 50 to 75mm on beds stops weeds, and 75 to 100mm holds in moisture.

Deeper is not better past 100mm. The mistake I saw most was a bed topped up every spring without the old layer being raked through first, until it sat 12 to 15cm deep. At that depth, rain struggles to reach the soil and the roots stay shallow. Keep bark 5 to 10cm back from stems and trunks too, so damp bark sitting against them cannot rot the stems.

For the full method, including how to prepare the bed, see my guide on how to lay bark chippings. For paths, the wood chip path guide covers edging and the sub-base. For hens, read wood chip for a chicken run.

How Much Does a Bulk Bag of Bark Cover?

A 1,000L bulk bag of bark covers about 13m² at 75mm, 10m² at 100mm and 40m² as a 25mm top-up.

These figures are before the 15% settling allowance, but the calculator does this for you. Bag names on their own tell you very little. Our builders bag is 600L on most bark and 700L on the hardwood chips, and other suppliers use different sizes again. When you compare two quotes, compare the litres.

How Do I Measure an Odd-Shaped Bed?

An odd-shaped bed is measured by choosing the nearest shape in the calculator (rectangle, circle, triangle or L shape) and taking two or four measurements.

• A round bed: measure straight across the middle, edge to edge.
• A triangle: measure one side as the base, then the height from that side to the opposite corner.
• An L-shaped border: split it into two rectangles and measure each, without counting the corner twice.
• A curved, wavy border: measure the length along the middle of the curve and take the average of three widths.

Measure in cm, or switch to imperial for feet and inches. Depth is always typed in mm in metric, so 7.5cm is 75mm.

How Much Bark Do I Need?

The bark you need is your area multiplied by your depth, plus 15% for settling, which gives the figure in litres to order.

Three worked examples, all run through the calculator above:

• A 5m x 2m border at 75mm is 10m² x 75mm = 750L. Add 15% and you need about 862L. In Border Bark, one 1,000L bulk bag covers it with 138L spare.
• An 8m x 1m path at 70mm is 560L. Add 15% and you need 644L. A 700L builders bag of Hardwood Chips covers it, with 56L spare. In Woodchip Mulch, where the builders bag is 600L, you would need a bulk bag instead.
• A 5m x 4m area at 100mm is 2,000L. Add 15% and you need 2,300L. In Woodchip Mulch, the cheapest order is one 60 x 60L pack (3,600L). The closest fit is four 600L builders bags (2,400L), which cost more.

How Much Extra Bark Should I Order?

Order 15% extra bark on top of the measured volume, because bark and wood chip settle once they are laid and walked on.

The calculator starts on 15% and lets you choose anything from 0 to 25%. I would use 0% for a top-up you can finish later from a few small bags, and 20 or 25% for a bed with a lot of foot traffic, or a chicken run where the hens scratch it about.

Topping up an existing layer is where people over-order most. Rake the old bark through first to loosen it and see how much is left. Most beds only need about 25mm on top, which is a third of a fresh bed.

Bulk Bag or Mini Bags?

A bulk bag of bark is usually cheaper per litre, while packs of small bags suit gardens with narrow or no side access. A bulk bag is dropped where the lorry can reach, usually the drive. From there you move it by wheelbarrow. A standard 85L wheelbarrow takes about 12 loads to empty a 1,000L bag. Small bags can be carried through the house or down a narrow side path, and any spare ones stack neatly in a shed for later. Untick "Bulk Bags" or "Mini Bags" in the calculator and the recommendation changes to suit.

Is Bark the Same as Wood Chip?

Bark and wood chip are different products: bark comes from the outer layer of the tree, and wood chip is the chipped timber itself. Bark lasts longer on a bed, looks tidier, and is what most people picture when they think of a mulched border. Wood chip is cheaper per litre, knits together underfoot, and is the better choice for paths and chicken runs. Both are worked out the same way in the calculator. If you are still choosing, see bark chippings for garden use, my comparison of decorative bark, or mulch or bark.

Why Do Weeds Grow Through Bark?

Weeds grow through bark when seeds land on top of it, or when perennial roots were left in the soil underneath. Bark smothers weed seeds that are already in the soil, as long as it is deep enough. It cannot stop new seeds blowing in and germinating in the top layer, so pull those while they are small. Dandelions, docks and bindweed come up from roots, so dig those out before the bark goes down. On a really weedy patch, a layer of plain cardboard under the bark does the job for the first season and then rots away into the soil.

What Should I Check When the Bark Arrives?

Fresh bark should smell of cut timber or earthy compost when you open the bag, and a sour smell means it needs airing first. Sour bark smells of rotten eggs, vinegar or ammonia, which means it has been stored wet and airless. Spread it out thinly to air for a few days before it goes near plants, because sour mulch can scorch leaves. For more on what can go wrong, see mulch problems.

Bark for a Play Area

Play bark and play chip are worked out on the play bark calculator, because the depth there is about safety, not looks. Choose any play product in the calculator above and it will take your measurements across for you. Outdoor Aggregates' play products were tested to EN 1177:2018 (the European standard for playground surfacing) and rated for falls above 3m at 100, 200 and 300mm deep. Go to the play bark calculator, or compare the options on play bark.

Next Steps

Put your measurements in the calculator, choose the box you want, and add it to your basket. If you are topping up, rake first and measure what is left.

If you would rather talk your bark and wood chip quantities through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

Got a bed that does not fit the shapes above? Leave a comment with the rough measurements and what the bark is for. I read every comment. I will reply with the litres I would order and the bag that suits.

Frequently Asked Questions

How much area does 100L of bark cover?

A 100L bag of bark covers about 1.3m² at 75mm deep, the usual depth for beds and borders. As a 25mm top-up, the same 100L covers 4m².

How many litres are in a cubic metre of bark?

A cubic metre of bark is 1,000L. A bulk bag of about 1,000L is roughly 1m³, which is why the two are often used to mean the same thing.

How much does 100L of bark weigh?

A 100L bag of bark weighs about 25 to 35kg, depending on how wet it is. Bark runs at roughly 250 to 350kg per m³, so a 1,000L bulk bag weighs somewhere around a quarter to a third of a tonne.

How many litres are in a tonne of wood chip?

A tonne of wood chip is about 3,100 to 4,900L. Dry spruce chip weighs about 206kg per m³ and wet chip about 320kg, so the wetter the chip, the fewer litres to the tonne. That is why the calculator works in litres, not tonnes.

How many wheelbarrows are in a cubic metre of bark?

A cubic metre of bark fills about 12 loads of a standard 85L wheelbarrow. Light bark heaps well, so you may manage it in fewer if you pile each load high.

Can I put bark straight onto soil?

Bark can go straight onto soil, and that is where it works best. Weed the bed, water it if it is dry, then spread the bark at 50 to 75mm. Over time the bottom layer rots into the soil and feeds it.

Should I put weed membrane under bark?

Weed membrane under bark is something I would leave out. The bark sits on top, dries out and blows about, and weeds still germinate in it from seeds landing on top. Bark at the right depth on weeded soil does the job on its own.