Mulch Calculator in Cubic Yards: How Much Mulch for Your Beds?

Mulch math is easy. What's not easy is hauling 40 bags from the store when you could've gotten a bulk delivery for half the price. I learned that one with a sore back and a trunk full of torn bags. Let's make sure you order right the first time.

The formula

Cubic yards = Length × Width × Depth ÷ 27

Feet for everything. Depth in inches divided by 12.

Say your bed is 20 ft × 4 ft and you want 3 inches of mulch:

1. 3" = 0.25 ft
2. 20 × 4 × 0.25 = 20 cubic feet
3. 20 ÷ 27 = 0.74 cubic yards → call it 1 yard

How deep? (This is the part people mess up)

I've seen both extremes: the sad half-inch sprinkle that does nothing, and the 6-inch mountain suffocating the plants. Here's what actually works:

• 3 inches — the sweet spot for weed control and moisture. This is what you want 90% of the time.
• 1–2 inches — fine for refreshing existing mulch that's faded. Don't pile fresh 3" on top of old 3".
• Around trees — 2–3", but pull it back 3 inches from the trunk. Those "mulch volcanoes" piled against bark? They rot the tree. I see them everywhere and it drives me nuts.
• Playgrounds — 6"+ of playground-rated mulch. Different product, different rules.

Less than 2" and the weeds just laugh at you. More than 4" and you're starving roots of air. Three inches. Trust me.

Bags vs. bulk (the money question)

Here's the conversion that matters: 1 cubic yard = 13.5 bags (the standard 2 cu ft bag).

• Our example (0.74 yd): that's 10 bags. Totally reasonable to grab bags.
• 2+ yards: stop. Call for bulk delivery. Bulk is often half the per-yard price of bags, and they dump it right in your driveway. I did the math once on 4 yards — bags would've cost me almost $400, bulk was $180 delivered.

My rule: under a yard, bags. Over two yards, bulk. Between one and two? Depends how much you enjoy loading bags into your car.

The settling thing nobody mentions

Fresh mulch settles. Like, 10–20% in the first month. So if you lay exactly 3", you'll have 2.5" by June.

Fix: lay it a little thick — 3.5" if you want to end at 3". Then hit it with a rake after a few weeks to fluff it back up. Don't over-order to compensate; you'll just end up with too much.

Quick numbers (at 3" depth)

| Bed | Yards | Bags (2 cu ft) | |---|---|---| | 10 × 4 ft | 0.37 | 5 | | 20 × 4 ft | 0.74 | 10 | | 30 × 6 ft | 1.67 | 23 | | 50 × 10 ft | 4.63 | 63 — get bulk! |

One last thing: don't mulch right against your house siding. Leave a few inches of gap — mulch holds moisture against wood, and termites love a mulch highway straight to your framing.

Too lazy for the math? (No judgment.) Our free mulch calculator spits out yards, bags, and cost in about ten seconds.