Mulch Calculator – How Much Mulch Do I Need?
Planning a garden project? Our free mulch calculator helps you figure out exactly how much mulch you need so you don’t buy too much or run short. Just enter your area dimensions and desired mulch depth to get your answer in seconds.
Mulch Calculator
How to Use the Mulch Calculator
- Enter the length of your garden bed in feet
- Enter the width in feet
- Enter the desired mulch depth in inches (2–4 inches is standard)
- Click Calculate
Mulch Coverage Formula
Cubic Yards = (Length × Width × Depth in inches) ÷ 324
One cubic yard covers approximately 100 sq ft at 3 inches deep.
How Much Mulch Do I Need? – Quick Reference
| Area (sq ft) | 2 inch | 3 inch | 4 inch |
|---|---|---|---|
| 100 sq ft | 0.62 cu yd | 0.93 cu yd | 1.23 cu yd |
| 200 sq ft | 1.23 cu yd | 1.85 cu yd | 2.47 cu yd |
| 500 sq ft | 3.09 cu yd | 4.63 cu yd | 6.17 cu yd |
Worked Example
A bed 25 ft long and 6 ft wide, mulched 3 inches deep:
- Area: 25 x 6 = 150 sq ft
- Depth in feet: 3 / 12 = 0.25 ft
- Volume: 150 x 0.25 = 37.5 cubic feet
- Cubic yards: 37.5 / 27 = 1.39 cubic yards
- In 2 cubic foot bags: 37.5 / 2 = 19 bags
Bulk delivery is usually cheaper than bags from around one cubic yard upwards, and it saves splitting and disposing of nineteen plastic sacks.
Mulch Types Compared
| Type | Lasts | Best for |
|---|---|---|
| Shredded hardwood | 1 to 2 years | General beds, knits together on slopes |
| Bark chips or nuggets | 2 to 3 years | Around trees and shrubs, slow to break down |
| Pine straw | 1 year | Acid-loving plants, very light to spread |
| Compost | Under 1 year | Vegetable beds, feeds the soil as it breaks down |
| Gravel or stone | Indefinite | Paths and xeriscape, adds no organic matter |
| Rubber mulch | 10 years plus | Play areas, does not improve soil |
Organic mulches break down and feed the soil, which is why they need topping up. Inorganic mulches last far longer but contribute nothing to soil health, and stone can raise soil temperature noticeably in hot climates.
How to Apply Mulch Properly
- Weed first. Mulch suppresses new weed seed germination but will not kill established perennial weeds underneath.
- Water the soil before mulching. Mulch slows evaporation, so it also slows rewetting of soil that is already dry.
- Keep it off the stems. Leave a 3 to 6 inch gap around tree trunks and plant stems.
- Fluff old mulch before topping up. Existing mulch often crusts over and sheds water. Rake it loose, then add only enough to return to your target depth.
Common Mulch Mistakes
- Applying too deep. More than about 4 inches can starve roots of oxygen and cause water to run off rather than soak in.
- Dividing cubic feet by 9 instead of 27. A cubic yard is 27 cubic feet.
- Using fresh wood chips on annual beds. Undecomposed wood can temporarily tie up nitrogen at the soil surface. It is fine around established trees and shrubs.
- Laying plastic sheeting underneath. It blocks air and water exchange and eventually degrades into shreds. Permeable landscape fabric, or nothing at all, works better.
Frequently Asked Questions
How much mulch do I need?
Multiply the bed length by its width to get square feet, multiply that by the depth in feet (inches divided by 12), then divide by 27 for cubic yards. A 25 x 6 ft bed at 3 inches deep needs 37.5 cubic feet, which is about 1.39 cubic yards or roughly 19 standard 2 cubic foot bags.
How deep should mulch be?
Two to three inches for most beds, and three to four inches around trees and shrubs. Going deeper than about four inches can starve roots of oxygen and cause water to run off the surface rather than soak in. Less than two inches will not suppress weeds effectively.
How many bags of mulch is 1 cubic yard?
About 13.5 bags of the standard 2 cubic foot size, since a cubic yard is 27 cubic feet. For 3 cubic foot bags it is 9 bags. Bulk delivery is usually cheaper from around one cubic yard upwards.
What type of mulch is best?
Shredded hardwood is the best general choice and knits together well on slopes. Bark chips last longer and suit trees and shrubs. Pine straw suits acid-loving plants. Compost is ideal for vegetable beds because it feeds the soil as it breaks down. Stone and rubber last far longer but add nothing to soil health.
Why should mulch not touch tree trunks?
Piling mulch against a trunk, sometimes called a mulch volcano, traps moisture against the bark, which encourages rot and fungal disease and invites rodents to gnaw the bark in winter. Leave a gap of 3 to 6 inches around trunks and stems so mulch forms a flat ring rather than a cone.
Does mulch go bad?
Organic mulch does not spoil, it simply decomposes, which is exactly what you want since it feeds the soil. It usually needs topping up every one to two years. Occasionally bagged mulch stored wet develops a sour smell from anaerobic conditions. Spread it out to air for a day before using it around plants.
Should I remove old mulch before adding new?
Usually not. Rake the existing layer to break up any crust, then add only enough new mulch to return to your target depth of two to three inches. Removing and replacing every year wastes material and throws away the partly decomposed layer that is actively improving your soil.