Mulch Calculator

What this mulch calculator does

This calculator estimates how much mulch you need to cover a garden bed in cubic yards, cubic feet, and 2 cubic foot retail bag count (the most common bag size at Home Depot, Lowe’s, and most independent nurseries). It defaults to a 3-inch depth — the sweet spot for residential beds — and applies a small 5 % waste factor because mulch is forgiving (extra mulch can always go into the next bed, around a tree, or onto a path).

How to use the mulch calculator

1. Measure the length and width of the bed in feet. For irregular curved beds, approximate as the longest length × the average width, or split into rectangles and run the calculator twice.
2. Enter the depth in inches. 3 inches is the default and the recommended residential depth. Use 2 inches for fresh beds that will be refreshed each spring, 4 inches around established trees and shrubs in very dry climates.
3. Pick Bulk yardage for a bulk delivery from a landscape supplier, or Bagged to see the equivalent 2 cubic foot bag count for a big-box-store buy.
4. Adjust the waste-factor slider. 5 % is the default; bump up for slopes and irregular bed shapes where the depth varies.
5. Read the result and tap Copy summary for a shopping list.

How much mulch you actually need

The math is short: cubic feet = sqft × (depth in inches ÷ 12). Convert to yards by dividing by 27 (since 27 cubic feet make one cubic yard) or to bags by dividing by 2 (each retail bag holds 2 cubic feet of compressed mulch). A few worked numbers:

Bulk delivery typically starts at 1 yard and gets cheaper per yard as the order grows. Bagged makes sense below about 1 yard, where the delivery fee wipes out the bulk savings, and for jobs that need to be hauled up stairs or through a narrow side gate where dumping a bulk pile in the driveway is impractical.

Choosing the right mulch type

Shredded hardwood is the workhorse. It breaks down to enrich the soil, knits together on slopes, and looks clean for a season. Refresh yearly.

Pine bark nuggets last longer than hardwood — two seasons before a refresh is needed — and look chunkier. Best for flat beds; nuggets wash off slopes in heavy rain.

Dyed hardwood (red, black, brown) holds its colour for a single season. The dye is non-toxic, but the underlying wood is often recycled pallet shavings, so soil enrichment is minimal. Pure aesthetic choice.

Pine straw is regional — common in the US Southeast, almost unheard of elsewhere. Cheap, light, slightly acidic. Refresh every 1–2 years.

Rubber mulch lasts 5+ years and never breaks down. Some gardeners avoid it for organic-soil reasons; others love it for playgrounds and around playsets. Heat retention is a downside in hot climates.

Stone mulch (decorative gravel, river rock) is permanent. No refresh needed beyond occasional topping up. Doesn’t suppress weeds as well as organic mulch unless paired with landscape fabric underneath. Better for arid landscaping than for plants that need moisture retention.

Avoid the mulch volcano

The single biggest mulching mistake is piling mulch up against a trunk or stem in a cone shape — the so-called “mulch volcano.” The trapped moisture against the bark encourages rot, the dark environment invites borers and rodents, and the absence of mulch on the open soil around the tree means weeds still grow there anyway. Correct form: an even donut of mulch 3 inches deep, starting 2–3 inches out from the trunk and extending to the drip line of the canopy.

Why the depth matters

Below 2 inches, weeds push through. Above 4 inches, water has trouble penetrating and the lower layer goes anaerobic, releasing the sour smell that signals decomposing organic matter without oxygen. The 2–4 inch sweet spot lets the mulch do its three real jobs — suppress weeds, retain soil moisture, moderate soil temperature — without suffocating the plants underneath.

In dry climates, lean toward 4 inches around established perennials and shrubs to maximise water retention. In wet climates or heavy clay soils, stay closer to 2 inches so the soil can breathe between rains. New transplants do well at exactly 3 inches.

Privacy

This calculator does its arithmetic in JavaScript on your device. There is no fetch call, no analytics on the values you enter, no server-side logging. The page works the same way offline once loaded.