Measure length and width, then multiply by depth to find cubic yards

The standard way to measure for mulch is to find the square footage of the area you want to cover, then decide how deep you want the mulch layer. Multiply length times width to get square feet. Divide that number by 9 to convert to square yards. Then multiply by the depth in inches and divide by 36 to get cubic yards — the unit mulch is sold in.

If that math feels abstract, there is a simpler path: measure your space in feet, write down the depth you want in inches, and use an online mulch calculator. You enter the numbers and it gives you cubic yards. Most landscape supply yards have one on their website, and the math is the same regardless of which calculator you use.

Key Takeaways

  • Measure the length and width of each bed in feet, then multiply those numbers together to find square footage.
  • Most mulch works best at 2 to 4 inches deep — shallower and weeds push through, deeper and you waste money and risk root rot.
  • Divide your square footage by 9 to get square yards, then multiply by your desired depth in inches and divide by 36 to get cubic yards.
  • Mulch is priced and delivered by the cubic yard, so knowing this number before you call a supplier saves time and prevents over-ordering.
  • Irregular shapes are easier to break into rectangles and add the results together than to estimate by eye.

Break irregular beds into rectangles

Most garden beds are not perfect squares. If your bed is L-shaped, curved, or has corners cut out, divide it into rectangles on paper first. Measure each rectangle separately, multiply length times width for each one, then add all the square footages together.

For a curved edge, measure the longest and widest points as if the curve were a straight line, then subtract a rough estimate of the area you are not actually covering. This does not need to be exact — mulch suppliers expect you to round up slightly, and a small overage is normal.

If you have multiple beds, measure each one separately and add the totals. Do not try to estimate the whole yard at once.

Choose your depth based on mulch type and purpose

Mulch depth matters because it controls how well it suppresses weeds and how long it lasts. At 2 inches, mulch blocks most weeds but breaks down faster and may need topping up yearly. At 3 to 4 inches, it lasts longer and stops more weeds, but costs more and can trap moisture against plant stems if piled too close.

Never pile mulch directly against tree trunks or shrub stems — leave a 3 to 4 inch gap around the base. Mulch touching wood promotes rot and invites pests. The depth you measure should be the depth across the open soil, not including this gap.

For new beds with bare soil, start at 3 inches. For beds you are topping up yearly, 2 inches is usually enough. For paths or areas where you want long-term coverage with minimal maintenance, go to 4 inches.

Account for settling and decomposition

Mulch settles and breaks down over time, especially in the first few months. Wood chips settle about 10 to 15 percent in the first year. Shredded bark breaks down faster. If you are ordering mulch for a new bed, add 10 to 15 percent to your cubic yard total to account for this.

If you are topping up an existing bed, you do not need to add extra — you are just filling the gap left by last year's mulch breaking down. Measure the depth you want the final layer to be, not the depth of what is already there.

Convert your measurements to cubic yards before ordering

Mulch is sold by the cubic yard, not by the bag or by weight. One cubic yard covers about 100 to 110 square feet at 3 inches deep. If your bed is 200 square feet and you want 3 inches of mulch, you need roughly 2 cubic yards.

The exact formula is: (square feet ÷ 9) × (depth in inches ÷ 36) = cubic yards. Or use a calculator and enter your numbers. Most suppliers will ask you for cubic yards when you call or order online, so have that number ready.

If you are buying bagged mulch instead of bulk, one 2-cubic-foot bag covers about 8 square feet at 3 inches deep. Divide your total cubic yards by 0.074 to find how many bags you need. Bagged mulch costs more per cubic yard but works if your bed is small or you do not have a place for a bulk delivery.

Measure twice if you are ordering bulk delivery

Bulk mulch is cheaper per cubic yard than bags, but a delivery truck holds a fixed amount and you pay for what you order. Measure your beds carefully before you call. If you order 5 cubic yards and only need 4, you have paid for mulch you do not use. If you order 4 and need 5, you have to place another order and pay another delivery fee.

Call the supplier and confirm their minimum order — some require 3 cubic yards, others will deliver 1. Ask whether they charge per cubic yard or per load. Some suppliers offer a small discount if you pick up instead of having it delivered, which saves money on small orders.

Frequently Asked Questions

How many bags of mulch do I need for 100 square feet?

At 3 inches deep, you need about 1 cubic yard, which is roughly 13 to 14 bags of 2-cubic-foot mulch. Bags vary slightly by brand and how tightly they are packed, so check the coverage listed on the bag itself. Buying 15 bags gives you a small buffer for settling.

What if my bed is oddly shaped or has islands in it?

Measure around the perimeter and treat it as a rectangle, then subtract the area of any islands (trees, rocks, or plants you are not mulching around). If the shape is too irregular to estimate, take a photo from above and sketch rectangles over it on paper, then add those rectangles together.

Do I need to measure depth differently for wood chips versus shredded bark?

No — measure the same way regardless of mulch type. Both work best at 2 to 4 inches. Shredded bark breaks down faster and may need replacing sooner, but the initial depth measurement is the same. Check with your supplier about how quickly their specific product settles.

Can I just eyeball how much mulch I need?

You can, but you will almost always order too much or too little. Eyeballing a 200-square-foot bed is harder than it looks, and mulch costs add up quickly. Spending five minutes with a tape measure and a calculator saves money and prevents a second trip to the supplier.

What if I am not sure whether to order 3 or 4 cubic yards?

Round up. Extra mulch can go in other beds, be stored for next year, or spread thinner than planned. Ordering too little means a second delivery fee or a trip back to the store. Most suppliers expect slight overage and it is normal to have a small amount left over.