Measure your garden beds first
The only way to know how much mulch to buy is to measure the area you plan to cover. Start by measuring the length and width of each garden bed in feet. If your bed is rectangular, multiply length by width to get the square footage. If it's an irregular shape, break it into rectangles, measure each one separately, and add the totals together.
Write down each measurement. You'll use these numbers to calculate volume, and it's straightforward to forget a bed or misremember a size once you're at the garden center. Take a photo of your notes or snap pictures of the beds themselves so you have them with you when you shop.
Key Takeaways
- Measure the length and width of each bed in feet, multiply them together, and add all the square footage totals to get your total coverage area.
- Most mulch for garden beds should be 2 to 3 inches deep; use 2 inches for annual beds and 3 inches for perennials or areas with heavy weeds.
- Divide your total square footage by 100 to find how many cubic yards you need (this accounts for the standard 2-inch depth).
- Mulch is sold by the cubic yard, cubic foot, or bag; a cubic yard covers roughly 100 square feet at 2 inches deep, and a 2-cubic-foot bag covers about 8 square feet.
- Add 10 to 15 percent extra to your calculation to account for settling and uneven ground.
Decide on your mulch depth
The depth of mulch you lay down affects how much you need to buy. Most garden beds work well with 2 to 3 inches of mulch. Two inches is standard for annual flower beds and vegetable gardens where you'll be replanting each year. Three inches is better for perennial beds, shrub borders, or areas where weeds are a persistent problem—the extra depth suppresses more weed seeds.
Don't go deeper than 4 inches unless you're dealing with a severe weed problem. Too much mulch can trap moisture against plant stems and roots, leading to rot. It can also prevent water from reaching the soil underneath. Stick to the 2- to 3-inch range for most situations.
Convert square footage to cubic yards
Mulch is sold by volume, not by area, so you need to convert your measurements. The standard formula is straightforward: divide your total square footage by 100. This gives you the number of cubic yards you need for a 2-inch depth.
Here's why: one cubic yard of mulch spread 2 inches deep covers approximately 100 square feet. If your beds total 200 square feet, you need 2 cubic yards (200 ÷ 100 = 2). If your beds total 350 square feet, you need 3.5 cubic yards (350 ÷ 100 = 3.5).
If you want 3 inches instead of 2, multiply your cubic yard total by 1.5. For example, 2 cubic yards at 2 inches becomes 3 cubic yards at 3 inches (2 × 1.5 = 3).
Understand mulch sales units
Mulch comes in three main formats, and the one you choose affects how you shop. Cubic yards are the standard for bulk mulch delivered by truck or picked up in your own vehicle at a garden center. One cubic yard is a pile roughly 3 feet long, 3 feet wide, and 3 feet tall. Cubic feet are smaller units—27 cubic feet equal 1 cubic yard—and some garden centers sell mulch this way by the scoop or bucket.
Bags are the most convenient for small areas. A standard mulch bag holds 2 cubic feet. To cover 100 square feet at 2 inches deep, you need about 13 bags (100 square feet ÷ 8 square feet per bag = 12.5, rounded up). Bags cost more per cubic foot than bulk mulch, but you avoid delivery fees and don't need to store a large pile.
For areas under 100 square feet, bags usually make sense. For 100 to 300 square feet, compare the price of bulk mulch plus delivery against bagged mulch. For anything over 300 square feet, bulk is almost always cheaper.
Account for settling and uneven ground
Mulch settles over time as it breaks down and compacts, especially in the first few weeks after you lay it. It also sits unevenly on ground that slopes or has dips. Add 10 to 15 percent extra to your calculation to make sure you have enough to top up bare spots and maintain your target depth through the season.
If your calculation came to 3 cubic yards, buy 3.3 to 3.5 cubic yards instead. The extra mulch is inexpensive insurance against running short, and any leftover can go into a storage pile for next year or be spread thinly in other areas of your yard.
Use a quick reference table for common bed sizes
| Bed Size (Square Feet) | Cubic Yards at 2 Inches | Cubic Yards at 3 Inches | Number of 2-Cubic-Foot Bags |
|---|---|---|---|
| 50 | 0.5 | 0.75 | 7 |
| 100 | 1 | 1.5 | 13 |
| 200 | 2 | 3 | 26 |
| 300 | 3 | 4.5 | 39 |
| 500 | 5 | 7.5 | 65 |
Frequently Asked Questions
What if my garden beds are oddly shaped?
Divide the bed into straightforward shapes—rectangles and triangles—measure each one, and add the square footage together. For a triangle, multiply the base by the height and divide by 2. For a circle, multiply the radius by itself, then multiply by 3.14. Breaking it into pieces makes the math manageable.
Can I use the same calculation for wood chips and bark mulch?
Yes. Wood chips, bark mulch, and shredded hardwood mulch all follow the same volume-to-coverage ratio. The type of mulch doesn't change how much area one cubic yard covers at a given depth. Choose the type based on appearance and how long it lasts, not on coverage math.
Should I measure around trees and shrubs that are already planted?
Measure the entire bed area, then subtract the space taken up by tree trunks and shrub stems if you want to be precise. In practice, most people measure the whole bed and buy accordingly—the small amount of mulch you don't use around stems is negligible and accounts for some of the settling buffer you're already adding.
What if I'm not sure whether to use 2 or 3 inches?
Start with 2 inches. It's the standard depth for most beds and suppresses weeds effectively. If you find weeds breaking through by mid-summer, you can add another inch the following year. It's easier to add mulch later than to remove excess.
Do I need to remove old mulch before adding new mulch?
No. If your old mulch is still in decent condition, you can spread new mulch on top. If it's heavily decomposed or matted down, rake it out first. Either way, this doesn't change your calculation—measure the bed as it is now and calculate based on the depth you want to achieve after you spread the new mulch.