Estimate mulch volume for a rectangular bed

As with aggregate, volume is L × W × T in meters. Default waste is lower (5%): you do not compact mulch with a plate. The material still slumps on its own (rain, decay, foot traffic). The result is also in liters (1 m³ = 1,000 L) and 50 L bags, a common garden-center size. Typed thickness is capped at 50 cm: beyond that it is no longer surface mulch. US bulk mulch is often sold by the cubic yard: 1 m³ ≈ 1.31 yd³.

V = L × l × e

Vmarge = V × (1 + p / 100)

litres = Vmarge × 1 000 ; nsacs = litres / 50

The rectangle approximates a bed. An irregular border uses an average width, or zones. Bark, chips, flax straw, or rubber crumb do not share density or settlement: the math does not convert to kilograms, because no single density is defensible. Maker sheets often give a volume (50 L, 2 cu ft) and a thickness range. A layer too thick against a woody stem is a cultural problem, not a formula problem.

Length

Length of the bed along the hedge or fence. For a circle, compute area separately (πr²) then multiply by thickness: this tool stays rectangular.

Width

Mulched width, excluding plants if you leave a bare basin at the collar.

Thickness

Thickness you want today. 7 cm of fresh bark can fall toward 4–5 cm after a winter. Type spread thickness, not “in six months.”

Margin (settlement, losses)

5% covers bag losses and a slight surplus. A very fluffy product (straw) settles more: raise the margin or plan a top-up rather than an oversized first layer.

Assumptions

• Rectangular area of uniform thickness.
• No mass conversion: only volume and 50 L bags are calculated.
• The lump margin does not replace the product’s real settlement.

Limits

• Mulch type (bark, cocoa, flax, slate) is not distinguished.
• 70 L bags or bulk supersacks are recalculated from the displayed liters.
• Basins at plant collars and unmulched paths are not deducted automatically.

21 bags of 50 L is 1.05 m³: check whether the garden center sells bulk cheaper at that volume. After placing, the level drops. A spring top-up is better than a 15 cm layer packed against collars. For decorative gravel in the same bed, switch to the gravel tool: density and settlement have nothing in common.

• Typing 5 for 5 cm of thickness.

  The unit is the meter. 5 cm = 0.05 m. Typing 5 would be a 5 m layer, rejected by the 0.5 m maximum.

• Counting 50 L bags as if they were 2 cu ft bags without converting.

  The result divides liters by 50. For 2 cu ft bags (~56.6 L): liters / 56.6.

• Thickening heavily “so I never come back.”

  Mulch settles and decays. An excessive layer against a collar smothers. Plan a top-up.

• Gravel calculatorFor a base course, a path, or drainage: volume comes from the box, mass applies 1,600 kg/m³. That is an order of magnitude; delivered crushed stone can be heavier or lighter.
• Paint calculatorQuantity is a division: net area times number of coats, divided by spreading rate in square meters per liter. Spreading rate is read on the product sheet and depends on the substrate.
• Concrete calculatorThe math starts from a rectangular box: volume in m³, then a waste margin. Mass uses 2,400 kg/m³, a typical normal-weight concrete density, not every mix.

Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

• Pratiques courantes de calepinage et pertes en travaux (peinture, sols, granulats) — Documents techniques unifiés / fiches fabricants