Mulch Calculator

Mulch Calculator: How Much Mulch Do You Really Need?

In the above mulch calculator type in the size and depth of your bed. In about ten seconds, you’ll get the answer. You can use it to know exactly what to ask for when you go to a garden shop or a supplier’s yard. It tells you how many cubic yards to order in bulk and how many bags to buy. If you want to skip the steps and go straight to the coverage table, you can see at a glance what most home gardens are covered. 

It’s a free mulch calculator, and you don’t even have to sign up. After that, it gets more in-depth: the math behind the numbers, how to deal with round and oddly shaped beds, how much a yard of mulch really costs after delivery, and why the math for rubber mulch is so different.

Quick Answer: How Much Mulch Do I Need?

Here is the number almost everyone comes here for.

One cubic yard of mulch covers:

How to use it: measure your bed in square feet, pick your depth, and divide.

A 200 square foot bed at 3 inches deep needs 200 ÷ 108 = 1.85 cubic yards, or about 25 bags.

One more number worth memorizing: one cubic yard is equal to 13.5 standard bags, which are the size that most garden stores sell in 2 cubic foot units. Let’s say a supplier gives you a quote for 3 yards. That’s equal to about 41 bags that you would have to lift into your car otherwise.

Which depth should you pick? Almost always, two to four inches is enough:

• 2 inches for beds with plants that are weak or have short roots
• Most flower beds and plant borders should be 3 inches deep. This is also the best choice for stopping weeds in general.
• 4 inches for paths or bare beds with a lot of weeds

Don’t go more than 4 inches. Roots can drown if there is too much water on them from thick dirt. Also, don’t pile mulch up against plant stems or tree trunks; keep it 2 to 3 inches away from them.

How to Calculate How Much Mulch You Need (The Formula)

When your depth is the same as one of the rows, the quick table will work. Do the math when it doesn’t work.

In feet, cubic yards are equal to (length x width x depth) ÷ 27.

People get the depth part wrong. The first number is in inches, and the other two are in feet, so divide it by 12 to get the other numbers.

• 2 inches times 12 is 0.17 feet
• 3 inches times 12 is 0.25 feet
• 4 inches times 12 equals 0.33 feet

It worked for a 20-foot-by-8-foot bed that was 3 inches deep.

1. Step 1: Figure out how deep it is: 3 times 12 is 0.25 feet
2. Step 2: Multiply 20 by 8 times 0.25 to get 40 cubic feet.
3. Step 3: Split the number 40 by 27 to get 1.48 cubic yards.
4. Step 4: Or, put it in bags: 40 divided by 2 equals 20 bags

Mulch calculator yard math: why you divide by 27

People get lost at the “divide by 27” step, so here’s where it comes from. Three feet is a yard. There are three feet of space on each side of a cubic yard, so three times three times three is twenty-seven cubic feet.

Loose mulch sellers who bring in trucks sell in cubic yards. The bags in the store are marked with cubic feet. That’s the only reason for the change, and it’s also the mistake people make most often when they try to figure out mulch by hand. You missed this step if your answer looks 27 times too big.

When you place your order, round up. The ground is never perfectly flat, and beds are never perfectly square. It is normal to add 5 to 10 percent, which turns that 1.48-yard job into a 1.5- or 2-yard order.

Are you doing a full gardening job? For the layers below, our topsoil calculator, mulch calculator and gravel calculator both use the divide-by-27 method.

Mulch Calculator for Irregular or Circular Beds

Most real gardens are not rectangles. Here is how to handle the two common cases.

Circular beds and tree rings

For every π, multiply the radius by the depth in feet.

Use 3.14 for π. Radius is half of the width, and the mistake to watch out for is forgetting to cut the diameter in half.

A tree ring that is 4 feet across and 3 inches deep is an example.

Step 1: Square the radius, which is 4 times 4.

Step 2: Multiply 3.14 by 16 times 0.25 to get 12.57 cubic feet.

Step 3: Multiply 12.57 by 27 to get 0.47 cubic yards.

Step 4: Divide 12.57 by 2 to get 6.3, which means you need to buy 7 bags.

There isn’t much to worry about if your tree ring looks like a donut with a hole in the middle. It’s cheaper to buy an extra half bag than to run out.

Irregular and curved beds

Do not try to figure it out. Cut the bed into rough circles and squares, figure out each one, and then add them all up.

If the curved edge of a fence neatly splits into two 12 ft x 4 ft and 6 ft x 3 ft sides,

• 12 times 4 is 48 square feet.
• 6 times 3 is 18 square feet.
• 66 square feet in total.

At 3 inches deep, 66 divided by 0.25 equals 16.5 cubic feet, which is 0.61 cubic yards or nine bags.

When measuring for a wavy edge, find the widest places and let yourself be a little off. You can throw away that extra anyway. It’s fine to pace over big areas; a normal adult step is about 3 feet.

How Much Is a Yard of Mulch? (Cost)

These are just rough estimates; you should call a local supplier before you buy because prices vary by area, season, and type of mulch.

Bulk mulch, delivered

Mulch in bags costs between $3.50 and $6.00 for a 2-cubic-foot bag.

The 20×8 bed (1.48 cubic yards, 20 bags) could have either choice.

Round up to 1.5 yards for bulk. That costs $45 per yard, which adds up to $128 when you add the $60 delivery fee.

Bagged: 20 bags costing $4.50 each cost around $90, and you have to carry them yourself.

This time, Bagged wins, which shocks everyone. The flat delivery fee is very bad for small items. About 3 to 4 cubic yards is where the break-even point is. Buy bags below that. It quickly gets cheaper above that point, and by 5 yards, you’d have to lift 68 bags, which is not a good way to spend an afternoon.

Some tools are made just for one shop, like the Lowe’s mulch calculator, which is based on that store’s own bag sizes and products. If you already know what you want, those are helpful, but the cubic yard math on this page works the same way no matter what store you buy from.

Rubber Mulch Calculator: Different Material, Different Math

The organic method will give you a very bad number when you try to figure out how much rubber mulch you need.

What makes it different:

• It is sold by the bag space it takes up, not by the free cubic yards. 
• Getting rubber mulch in bulk is not common.
• Bags are usually 0.8 cubic feet instead of 2 cubic feet.

For gardening, it only needs 1.5 to 2 inches of depth because it doesn’t break down or compress like wood does.

It’s heavy. A bag that’s 0.8 cubic feet in size weighs 30 to 40 pounds.

Coverage: A 0.8-cu ft bag fills up about 4.8 square feet when stacked 2 inches deep.

As an example, the same 20-foot-by-8-foot area covered in rubber mulch

• Step 1: Find the size of the bed (20 x 8 = 160 square feet).
• Step 2: Buy 34 bags because 160 ÷ 4.8 = 33.3

For the same bed, that’s about 20 bags of wood mulch. Also, 34 bags cost between $340 and $510, and a bundle of wood costs around $90. It costs $10 to $15 for each bag.

It costs time. Wood mulch breaks down over time, so you need to add more every year. The extra cost is spread out over 10 years because rubber mulch lasts that long. Aside from that, it doesn’t feed the soil like wood that breaks down does. This is important in planting beds but not so much on walks or around playground equipment.

There is a separate calculation for playgrounds. If you put a rubber mulch calculator under a swing set or a climbing frame for safety, you need a lot more depth. Usually, you need 6 inches. The right depth varies on how high the equipment falls. At 6 inches, that 160-square-foot area needs 100 bags, not 34. Before you place your order, make sure you read the CPSC public playground safety guide and the manufacturer’s instructions for your equipment.

FAQs

Q1. How many bags of mulch do I need for my yard?

Take your cubic feet and divide it by 2 to get the size of a standard bag. There are 40 cubic feet in a 20×8 bed that is 3 inches deep, which means that there are 20 bags. If you know the answer in cubic yards, you just need to multiply it by 13.5, since one cubic yard is equal to 13.5 standard bags. Get an extra and buy one.

Q2. What depth of mulch should I use?

Most things can be done with two to four inches. As a general rule, flower beds and plant borders should be 3 inches deep, as that is the depth that keeps weeds out. Drop to 2 inches around plants with weak roots or that are easily damaged. Do not pile dirt up against tree or plant stems. Allow the bark to breathe by leaving a gap of 2 to 3 inches.

Q3. How much does a yard of mulch cost?

Most of the time, basic oak mulch costs $30 to $50 per cubic yard and cedar or premium bark costs $50 to $80. There is also a $50 to $100 delivery fee per trip. Each 2 cu ft bag of mulch costs between $3.50 and $6.00. Bags cost less until you need 3 to 4 yards because delivery is a flat fee.

Q4. Is rubber mulch calculated the same way as wood mulch?

No, rubber mulch is not sold in loose cubic yards. Instead, it is sold by the bag covering. The bags are about 0.8 cubic feet in size, and the mulch goes down less deeply. At 2 inches, one bag covers about 4.8 square feet. About 34 rubber bags are needed for a 160-square-foot bed, but only 20 3-inch wood bags are needed.

Q5. How often do I need to add more mulch?

Soil can be mixed in with organic mulch like straw, bark, or wood chips. Add more mulch once a year, usually in the spring. A whole new layer isn’t needed very often. Check to see how much is left. If there is only one inch left and you need three, you only need to buy for the two-inch difference. Rubber mulch doesn’t break down, and you don’t have to worry about it for ten years.

Q6. Can I use this calculator for a circular garden bed?

Yes. Put the tool in circle mode and type in the radius, which is half of the width of the circle. To find the volume by hand, multiply π by radius² times depth in feet and then split by 27. A tree ring that is 4 feet around and 3 inches deep takes up 12.57 cubic feet, which is about 7 bags.

Conclusion

It all comes down to three numbers: the size of your bed, how deep it is, and 27. Take the length of the bed and multiply it by three, unless there’s a good reason not to. Then, divide that number by 27 for cubic yards or by 2 for standard bags. It took 1.48 yards to build the 20×8 bed. It took about half a yard to make the tree ring. It took 34 bags instead of 20 for that same 20×8 bed of rubber mulch. 

What you need to do is easy after the first time you do it. Use the mulch calculator at the top of this page to get your own measurements. If the ground is uneven, round up by 5 or 10 percent, and order everything at once instead of going back and forth between trips.