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Mulch Calculator

Bed area and depth to cubic yards or bags of mulch needed, and cost.

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Your bed

Mulch needed

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2 to 3 inches is the sweet spot

Less than 2 in of mulch does little to block weeds or hold moisture; more than 3 to 4 in can suffocate roots and hold too much moisture against a plant's crown. Refresh to 2-3 in each year rather than piling new mulch on top of old.

Volume is length times width times depth, with depth converted from inches to feet before multiplying. Bulk mulch is sold by the cubic yard (27 cu ft), which is usually cheaper per unit than bagged mulch for anything beyond a small bed, though it requires somewhere to dump and a way to move it.

Bagged mulch is commonly sold in 2 cu ft bags, so dividing your total cubic feet by 2 gives bag count. Always round up, since a partial bag still means buying a whole one.

Keep mulch a few inches back from tree trunks and plant stems ("no volcano mulching") — piling it against the base traps moisture against the bark and invites rot and pests.

Where these numbers come from

These are planning estimates. Check product labels, your local building code, and a licensed contractor before you buy materials or build.

Frequently asked questions

Bulk or bagged, which is cheaper?

Bulk mulch delivered by the cubic yard is almost always cheaper per unit for anything more than a couple cubic yards, but it requires a delivery spot and a wheelbarrow or similar to move it. Bagged is more convenient for small beds or no-truck-access situations.

How often should I add new mulch?

Most organic mulch breaks down and should be refreshed to a full 2-3 in depth once a year; add only enough to reach that depth rather than piling a full new layer on top of what's already there.

Does mulch type change how much I need?

The volume math is the same regardless of type (wood chips, bark, straw), but very light materials like straw settle and compact faster, so you may need to add more sooner to maintain the same depth.

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