Calculate cubic metres, cubic yards and litres of mulch, topsoil, compost, gravel or any bulk material — converted to common bag sizes and bulk volumes, with a depth cross-section visualizer. Metric and imperial.
What Your Results Mean
Choose your bed shape first. For rectangular beds — the most common — measure the longest side as length and the perpendicular side as width. For circular beds (tree rings, round planters), measure from the center of the bed to the outer edge; that's your radius. If your bed is irregularly shaped, break it into rectangles and circles, calculate each separately, and add the volumes together.
Depth matters more than most gardeners realise. Five centimetres (2 in) is the minimum for weed suppression; 7.5 cm (3 in) is the residential standard that balances coverage with material use; 10 cm (4 in) is recommended for new beds or aggressive weed control. Anything over 10 cm risks suffocating plant roots and is wasteful — mulch decomposes from the bottom, so deeper mulch doesn't last proportionally longer. For topsoil in raised beds, fill to the bed depth (typically 20–30 cm).
The bulk-versus-bagged choice is mostly logistics. Bagged material is easy to transport in a family car and carry to the bed one bag at a time, but a large project needs dozens of bags. Bulk delivery needs truck access (driveway or front garden) and a wheelbarrow to move material, and many suppliers have minimum delivered volumes. As a rough rule, projects above about 2 cubic metres usually justify a bulk delivery; smaller top-ups suit bags.
Material Density Reference
The calculator works for any bulk material sold by volume, but weights vary dramatically. Knowing the weight helps you plan delivery logistics and equipment:
- Mulch (bark): 400–600 lb per cubic yard. Lightweight, easy to wheelbarrow.
- Topsoil: 1,800–2,200 lb per cubic yard when dry; up to 2,700 lb when wet. Heavy.
- Compost: 900–1,200 lb per cubic yard. Medium weight.
- Sand: 2,400–2,700 lb per cubic yard. Very heavy — one cubic yard maxes out a half-ton pickup.
- Gravel (3/4" minus): 2,400–2,800 lb per cubic yard. Very heavy.
Pro Tip
Schedule bulk delivery on a day you can spread the material immediately. A pile of mulch sitting on your driveway for a week kills the grass underneath, and wet topsoil piled on pavement stains the surface. Most suppliers will tarp the load on request if rain is forecast.
The Math Behind the Calculator
Mulch and topsoil estimating starts with coverage area, multiplies by depth, and converts to cubic yards. The shape of the bed affects only the area calculation:
// Rectangle bed
area_sq_ft = length_ft × width_ft
// Circle bed
area_sq_ft = π × radius_ft² (π ≈ 3.14159)
// Convert depth to feet
depth_ft = depth_inches / 12
// Volume in cubic feet
volume_cubic_ft = area_sq_ft × depth_ft
// Convert to cubic yards (27 cu ft = 1 cu yd)
volume_cubic_yd = volume_cubic_ft / 27
// Convert to cubic meters
volume_cubic_m = volume_cubic_ft × 0.0283168
Bag Count
Standard bagged mulch is sold in 2 cubic foot bags. To convert cubic feet to bags:
bags_needed = ceil(volume_cubic_ft / bag_size_cu_ft)
// For 2 cu ft bags: bags = ceil(volume_cubic_ft / 2)
Some suppliers sell 1.5 cu ft bags of premium hardwood mulch — adjust the bag size input accordingly.
Volume & Bag Formulas
Volume is area multiplied by depth, converted between unit systems. Bags are total litres divided by the bag size you selected:
volume_m³ = area_m² × depth_m
litres = volume_m³ × 1000
bags = ceil(litres ÷ bag_size_litres)
1 cubic yard = 0.7646 m³
Bag Sizes Around the World
Bag sizes differ by country — the calculator covers the common ones. What to expect at the garden centre:
- North America: 2 cu ft (56.6 L) bags are the garden-centre standard.
- Metric countries (UK, Europe, South Africa, Australia, New Zealand): 40–60 L bags are typical.
- Bulk delivery: sold by the cubic metre (or cubic yard in the US) — ask your supplier about minimum delivered volumes.
- Loose vs settled: bulk material settles after spreading; the 10% allowance covers it.
Assumptions & Limitations
Every number above rests on these constants. If your project differs, change the matching input — or read the linked guide for the full reasoning.
- Bulk mulch sells by the cubic yard (27 cu ft)
- Standard bags are 2 cu ft; premium bagged mulch is often 3 cu ft
- Depth is applied over the whole bed area
- Quantities are for material only — settling and spreading losses are covered by the allowance you choose
Worked Example: 20×5 Foundation Bed at 3" Depth
A typical front-foundation planting bed: 20 feet long, 5 feet wide, mulch at 3 inches deep. Let's run the numbers:
- Area: 20 × 5 = 100 sq ft.
- Depth in feet: 3 ÷ 12 = 0.25 ft.
- Volume: 100 × 0.25 = 25 cubic ft = 0.93 cubic yards (round to 1 yard for ordering).
- Bags needed: 25 ÷ 2 = 12.5 → 13 bags of 2 cu ft.
- Volume: 100 sq ft × 3 in = 25 cu ft ≈ 0.71 m³ (0.93 yd³).
- In 50 L bags: 710 ÷ 50 = 15 bags, carried to the bed one at a time.
- In bulk: about 0.7 m³ — many suppliers round up to a 1 m³ minimum delivery, so ask before ordering.
Now consider a larger project: a 15 m × 2.4 m (50 × 8 ft) bed at 7.5 cm (3 in) deep. That's 36 m², about 2.8 m³ (3.7 yd³) — 56 of the 50 L bags, or one bulk delivery. At this size the truck saves dozens of wheelbarrow trips; that is the real argument for bulk.
The break-even point is typically around 2 cubic yards (27 cubic feet = 14 bags). Below that, bags are reasonable, especially if you don't have truck access or can't physically move a 1,000-pound pile. Above 2 yards, bulk is almost always the right call.
Reminder
Bulk delivery requires a place for the truck to dump. Most suppliers need at least 10 feet of vertical clearance and a 10-foot-wide access path. If the truck can't reach your backyard, plan to dump in the driveway and wheelbarrow — add 30 minutes of labor per cubic yard for moving.
