The amount depends on how deep you spread it

For 100 square feet, you need between 0.5 and 1.5 cubic yards of mulch. The exact amount depends on how thick you want the layer — most gardeners use 2 to 4 inches deep. At 2 inches deep, you need about 0.6 cubic yards. At 3 inches, you need about 1 cubic yard. At 4 inches, you need about 1.3 cubic yards.

Depth matters because it controls how well the mulch blocks weeds and holds moisture. Too thin (under 2 inches) and weeds push through. Too thick (over 4 inches) and you risk trapping moisture against the soil and rotting plant stems. Three inches is the middle ground most people choose.

Key Takeaways

  • A 100 square foot area at 3 inches deep needs 1 cubic yard of mulch, which is the standard depth for weed suppression and moisture retention.
  • Mulch settles over time, so order 10 to 15 percent more than your calculation to account for settling in the first few weeks.
  • One cubic yard covers roughly 100 to 150 square feet at 2 inches, or 75 to 100 square feet at 3 inches, depending on how densely you pack it.
  • Measure your bed length and width in feet, multiply them together to get square footage, then use the depth chart to find your cubic yardage.

How to calculate the exact amount for your space

Start by measuring your garden bed or area in feet. If your bed is rectangular, measure the length and width, then multiply them. A bed that is 10 feet long and 10 feet wide is 100 square feet. If your bed is oddly shaped, break it into rectangles, calculate each one, and add them together.

Once you have your square footage, use the depth you want to find cubic yards. The formula is: (square feet × depth in inches) ÷ 324 = cubic yards. For 100 square feet at 3 inches, the math is (100 × 3) ÷ 324 = 0.93 cubic yards, which rounds to 1 cubic yard. For 2 inches, it is (100 × 2) ÷ 324 = 0.62 cubic yards. For 4 inches, it is (100 × 4) ÷ 324 = 1.23 cubic yards.

Most mulch suppliers sell by the cubic yard, so round up to the nearest half yard. If your calculation gives you 0.62 cubic yards, order 1 cubic yard. If it gives you 1.23 cubic yards, order 1.5 cubic yards.

Account for settling when you place your order

Fresh mulch settles as it dries and breaks down over the first few weeks. You will lose roughly 10 to 15 percent of the volume. If you calculate that you need exactly 1 cubic yard, order 1.25 cubic yards instead to end up with the depth you want after settling.

This is especially true for bark mulch and wood chips, which settle more than shredded hardwood. Compost-based mulches settle even faster. If you are using a finer mulch, lean toward the higher end of the 10 to 15 percent range.

Different mulch types and how they spread

The type of mulch you choose affects how far it spreads and how long it lasts. Shredded hardwood mulch is dense and spreads evenly, so your calculations will be accurate. Bark nuggets are lighter and fluffier, so the same cubic yard will cover slightly more area but will settle more noticeably. Wood chips are coarser and settle less than bark but more than shredded hardwood.

Compost-based mulches and aged wood products break down faster than fresh bark or wood chips, so you may need to top them off sooner. If you are using compost as mulch, plan to refresh it every spring. If you are using bark or wood chips, you can usually go two to three years before adding more.

Spreading mulch evenly across 100 square feet

Spread mulch with a shovel or mulch fork, working in sections. Divide your 100 square foot area into four 25-square-foot sections and spread one quarter of your mulch in each section. This helps you see whether you are on track for even depth.

Rake as you go to level the surface and break up clumps. Keep mulch 3 to 4 inches away from tree trunks and plant stems — mulch piled against wood can trap moisture and cause rot. A common mistake is piling mulch in a volcano shape around trees; instead, spread it in a flat, even layer that tapers away from the base.

What to do if you order too much or too little

If you order more than you need, store the extra in a dry place. Mulch keeps for several months if it stays dry, though it may start to break down or develop mold if it sits wet. A tarp over a pile will keep rain off. You can use extra mulch to top off the same bed next spring or spread it in a new area.

If you order too little, you have two options. You can order more and blend it with what you have — the color may not match perfectly, but it will even out as the mulch ages. Or you can spread what you have at a slightly thinner depth (2 inches instead of 3) and plan to add more next year. Thin mulch is better than no mulch, though it will not suppress weeds as well.

Frequently Asked Questions

Can I use less mulch if I put down landscape fabric first?

Landscape fabric blocks weeds better than thin mulch alone, so you can reduce depth from 3 inches to 2 inches and still get good weed control. However, fabric can trap moisture and prevent mulch from breaking down into the soil, so many gardeners skip it and rely on thicker mulch instead. If you use fabric, 2 inches of mulch over it is usually enough.

How often do I need to add more mulch to 100 square feet?

Bark and wood chip mulches break down over two to three years, so plan to add a 1 to 2 inch layer every spring or every other spring. Compost-based mulches break down faster and may need refreshing every year. You do not need to remove old mulch — just rake it level and add new mulch on top.

What if my bed is not a perfect rectangle?

Measure the longest length and widest width, multiply them, then subtract the square footage of any corners or sections you are not mulching. For an L-shaped bed, measure the vertical rectangle and horizontal rectangle separately, calculate each, and add them together. Rough estimates are fine — being off by 10 percent will not hurt.

Is 1 cubic yard of mulch heavy enough to deliver myself?

One cubic yard of mulch weighs 400 to 800 pounds depending on the type and moisture content. Bark mulch is lighter; compost-based mulch is heavier. Most people can shovel it into a truck, but delivery is worth the cost if you have back problems or a long distance to move it. Many garden centers deliver for a flat fee.

Can I use wood chips from my own tree trimming?

Yes, but let them age for at least three months before spreading them. Fresh wood chips pull nitrogen from the soil as they break down, which can slow plant growth. After three months, the breakdown slows and nitrogen loss becomes minimal. Shred them finely if you can — large chunks take longer to settle and break down.