Mulch Calculator
Find how much mulch a garden bed needs in cubic yards, cubic feet, and standard 2 cubic foot bags.
A 2 to 3 inch layer is the usual depth for garden beds. Bagged mulch comes in 2 cubic foot bags; larger jobs are cheaper bought as bulk cubic yards.
Enter the bed size and depth to find the mulch.
How to use the mulch calculator
Enter the length and width of the bed in feet and the depth you want in inches. The calculator returns the volume in cubic yards and cubic feet, and the number of standard 2 cubic foot bags so you can shop either way.
For a bed that is not a tidy rectangle, split it into sections, work out each one, and add the results. Round generously, since a thin spot in the coverage undoes much of the benefit mulch is there to provide.
How deep should mulch be
A layer of 2 to 3 inches is the sweet spot for most beds. That is deep enough to block light from weed seeds and slow water loss from the soil, while still letting air and rain reach the roots below.
Going much past 3 inches can do harm, trapping moisture against stems and starving roots of oxygen. Keep mulch a couple of inches clear of tree trunks and plant crowns rather than piling it up against them.
Bags or bulk by the cubic yard
Bagged mulch comes in 2 cubic foot bags, which are easy to carry and fine for a small bed or a few containers. The calculator rounds the bag count up, since a part bag still means buying a whole one.
For larger areas, bulk mulch sold by the cubic yard is usually cheaper per unit and saves opening dozens of bags. One cubic yard equals 27 cubic feet, or about 13 and a half of those retail bags, so the crossover comes quickly on a big project.
When and why to mulch
Late spring is a common time to mulch, once the soil has warmed but before summer weeds take hold. A fresh layer in autumn also helps insulate roots through winter cold in many climates.
Beyond weeds and water, mulch steadies soil temperature and breaks down over time to feed the soil. Organic mulches like bark and wood chips need topping up each year as the lower layer decomposes into the bed.
Frequently asked questions
- How much mulch do I need for 100 square feet?
- At a 3 inch depth, 100 square feet needs 25 cubic feet of mulch, which is about 0.93 cubic yards or roughly 13 of the standard 2 cubic foot bags.
- How deep should I spread mulch?
- Two to three inches works for most garden beds. That depth suppresses weeds and holds moisture without smothering roots. Deeper than three inches can trap too much moisture and harm plants.
- How many bags of mulch are in a cubic yard?
- A cubic yard is 27 cubic feet. With standard 2 cubic foot bags, that is about 13 and a half bags, so bulk delivery is usually more economical once a bed needs more than a few bags.
- When is the best time to mulch?
- Late spring is popular, after the soil warms but before summer weeds establish. A second application in autumn helps insulate roots over winter in colder climates.
- Does mulch need replacing?
- Organic mulches like bark and wood chips break down over time and feed the soil, so they need topping up roughly once a year to keep the layer at the depth you want.