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Garden & Outdoor

Mulch Calculator

How much mulch a bed needs in cubic yards, bags or a bulk load, and the depth that suppresses weeds without suffocating roots.

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Results update instantly as you type.

The bed
Add identical beds rather than working them out one at a time.
The mulch
Two inches suppresses weeds, four is the most roots will take.
Material
Topping up rather than starting bare. This is subtracted.
Buying
Bag size
Units
Measurement system
Prices are yours to set, so any currency works.

Everything is worked out in your browser, so the numbers never leave your device. The shareable link reopens the calculator with exactly these values.

Results

You need
0.74 cu yd of shredded bark
80 sq ft at 3 in deep, which is 10 bags or 0.74 cu yd bulk
Volume needed
20 cu ft
0.74 cu yd
Bags
2 cu ft each
10
Area covered
80 sq ft
Depth applied
3 in
Approximate weight
Dry. Wet bark can weigh half as much again.
370.4 lb
Cost in bags
10 x $4.5
$45
Cost in bulk
0.74 cu yd x $45
$33.33
Typical replacement
Top up about 1 in a year as it breaks down
every 2 years
iKeep it off the stemsPull the mulch back a couple of inches from trunks and crowns. Mulch piled against bark holds moisture there and rots it, which is what kills the plant, not the mulch itself.

Working

  1. area = 20 x 4 = 80 sq ft
  2. depth applied = 3 - 0 existing = 3 in
  3. volume = 80 sq ft x 3 / 12 = 20 cu ft
  4. cubic yards = 20 / 27 = 0.74 cu yd
  5. bags = 20 / 2 = 10, rounded up
  6. weight = 0.74 cu yd x 500 lb per cu yd = 370.4 lb

Quick answer

Mulch is bed area times depth. Work in feet and inches, divide by twelve to get the depth into feet, then by twenty seven to turn cubic feet into cubic yards. Three inches is the usual target: two suppresses weeds, four is as deep as roots will tolerate.

cubic yards = length ft x width ft x (depth in / 12) / 27

Worked example

Two beds, each 20 ft by 4 ft, going down 3 in deep in shredded bark.

Volume needed1.48 cu yd — 40 cu ft
Bags20 — 2 cu ft each
Area covered160 sq ft — 2 beds
Depth applied3 in
Approximate weight740.7 lb — Dry. Wet bark can weigh half as much again.
Cost in bags$90 — 20 x $4.5
Cost in bulk$66.67 — 1.48 cu yd x $45
Typical replacementevery 2 years — Top up about 1 in a year as it breaks down

Working

  1. area = 20 x 4 x 2 beds = 160 sq ft
  2. depth applied = 3 - 0 existing = 3 in
  3. volume = 160 sq ft x 3 / 12 = 40 cu ft
  4. cubic yards = 40 / 27 = 1.48 cu yd
  5. bags = 40 / 2 = 20, rounded up
  6. weight = 1.48 cu yd x 500 lb per cu yd = 740.7 lb

The bag count is the number that decides it. Twenty bags is a car load and a half at $90, against $67 for the same volume tipped on the drive, which is why bulk wins on anything over about a cubic yard even when the price per bag looks reasonable.

How much mulch per 100 square feet

Volume needed for a 100 sq ft bed at each common depth. Multiply by your own area over a hundred.

DepthUsed forCubic yards2 cu ft bags
2 inWeed suppression, minimum useful0.62 cu yd9
3 inStandard beds and borders0.93 cu yd13
4 inMaximum for planted beds1.23 cu yd17
6 inBare paths and around mature trees only1.85 cu yd25

Bags are rounded up. Suppliers sell bark by volume, not weight, so compare bags on cubic feet rather than on the price on the front.

At a glance

What it doesTurns bed size and depth into cubic yards, bags and a delivered weight
Inputs neededBed length and width, target depth, material
Main outputCubic yards and bag count
Formulacubic yards = area sq ft x (depth in / 12) / 27
CategoryGarden & Outdoor
CostFree, no sign-up, no download

How to use the Mulch Calculator

  1. Measure each bed and enter the length and width. For an irregular bed, break it into rectangles and add them as separate beds of the same total area.
  2. Set the depth. Three inches suits most planted beds; go to two if you are topping up annually.
  3. Enter any mulch still in place, so the tool works out what to add rather than what should be there.
  4. Compare the bag cost against the bulk cost with your own supplier's prices before ordering.

Frequently asked questions

How many bags of mulch in a cubic yard?

Thirteen and a half 2 cu ft bags, or eighteen 1.5 cu ft bags, because a cubic yard is 27 cubic feet. That is the conversion worth memorising: a yard of bulk replaces about thirteen bags.

How deep should mulch be?

Three inches for most beds. Two inches is the minimum that blocks enough light to stop weed seed germinating, and four inches is about the limit before you start starving roots of air and holding damp against stems.

How much does a yard of mulch weigh?

Shredded bark runs around 500 lb per cubic yard dry and noticeably more wet, wood chips around 600 lb, and compost around 1,000 lb. Rubber mulch is far heavier at roughly 1,400 lb.

Is bulk mulch cheaper than bags?

Almost always past a cubic yard, and the gap widens with volume. The catch is delivery: you need somewhere the truck can tip and a barrow route to the beds, so for a single small border bags still make sense.

How often does mulch need replacing?

Shredded bark thins out over about two years, wood chips three, compost within a single season. Rather than stripping and replacing, top up by about an inch each spring to hold the depth.

Volumes are exact; weights and coverage are estimates, because bulk material densities vary with moisture and how finely the material is shredded. Order a little over rather than under: settling and uneven ground both eat volume.

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