🌿 Mulch
🆓 Free
m³ / Bags / Tonnes
🌿 Mulch Calculator
Enter your garden bed dimensions and desired depth to instantly calculate cubic metres, number of bags, and total material cost. Add multiple beds to get a combined total, and compare the cost of bags versus bulk delivery to find the most economical option for your volume. Supports mulch, topsoil, compost, gravel, and sand.
🌿 Mulch / Fill Material Calculator
Material Type
Bed Shape
-
Total Volume Needed
🌱 Multiple Garden Beds
Add each bed or area to calculate combined total.
Bed / Area
L (m)
W (m)
Depth
When to Buy Bags vs Bulk
Bags vs Bulk Comparison
Bags are better when:
Volume under 1–2 m³
No vehicle/trailer for bulk delivery
Precise quantities needed
Easy access - no bulk truck access
Bulk (tonne bag / loose delivery) when:
Volume over 2 m³
Cost savings: bulk is 30–50% cheaper per m³
Large garden or multiple areas
Example: 3 m³ of mulch
Bags (70L at ₹350 each):
43 bags × ₹350 = ₹15,050
Cost per m³: ₹5,017
Bulk (₹3,500/m³ + ₹800 delivery):
3 m³ × 3,500 + 800 = ₹11,300
Cost per m³: ₹3,767
Saving with bulk: ₹3,750 (25%)
Run the calculator first to see your personalised comparison.
Depth Guide & Coverage
Volume Formula
Volume (m³) = Area (m²) × Depth (m)
Depth in mm divide by 1000 to get metres
50mm = 0.05m
Example: 6m × 2.5m bed, 50mm depth
Area = 6 × 2.5 = 15 m²
Volume = 15 × 0.05 = 0.75 m³
Bags needed = Ceil(Volume / Bag volume)
70L bags = 0.07 m³ each
Bags = Ceil(0.75 / 0.07) = 11 bags
1 m³ = 1000 litres = ~14 bags of 70L
1 tonne bag (bulk) ≈ 0.6–0.8 m³ (depending on material)
Frequently Asked Questions
Volume = Length × Width × Depth (all in metres). For a 6m × 2.5m bed at 50mm (0.05m) depth: 6 × 2.5 × 0.05 = 0.75 m³. Convert to bags by dividing by the bag volume: a 70L bag = 0.07 m³, so 0.75 ÷ 0.07 = 10.7 → buy 11 bags. Always round up - never round down. Add a 10% buffer for irregular shapes and settling. The calculator above does this for multiple beds and gives you the total across all areas.
New garden beds: 50–75mm (2–3 inches). Annual top-up of existing mulch: 25mm. Weed suppression in high-problem areas: 75–100mm. Tree circles and shrubs: 75mm (keep 5–10cm clear of trunk - mulch touching bark causes rot and disease). Pathways: 75–100mm. Vegetable gardens: 50mm without touching plant stems. Never apply so deeply that roots are smothered or mulch covers plant stems. Thick mulch can also harbour fungal disease and rodents in humid climates.
Under 1 m³: bags are almost always more convenient and often similar in price to bulk when delivery fees are included. 1–3 m³: compare total bag cost against bulk price plus delivery fee - bulk often wins but not always. Over 3 m³: bulk is typically 25–40% cheaper per m³ than bagged. Bulk requires good vehicle access, someone to receive delivery, and somewhere to temporarily store a large pile. Use the cost comparison feature in the calculator above to find the break-even point for your specific prices.
1 m³ covers: 40 m² at 25mm deep. 20 m² at 50mm deep. 13.3 m² at 75mm deep. 10 m² at 100mm deep. A 70L bag (0.07 m³) covers approximately 1.4 m² at 50mm or 0.7 m² at 100mm. So 1 m³ ≈ 14 × 70L bags. To find bags needed from your area: (Area × Depth in metres) ÷ 0.07 = bags of 70L. Always round up and add 10% for waste and settling.
Mulch (bark chips, straw, gravel) is laid on the soil surface. Purpose: suppress weeds, retain moisture, regulate temperature, improve appearance. Does not significantly improve soil fertility. Goes on top, not dug in. Topsoil is the upper layer of mineral soil with organic matter. Used to fill beds, level lawns, or improve growing conditions. Mixed into or laid as a growing medium - not typically used as surface mulch. Compost (decomposed organic matter) is richer in nutrients than topsoil and is best dug into soil before planting.
Wood chip/bark mulch: top up every 1–2 years as it gradually decomposes. Straw or shredded leaf mulch: every season - breaks down quickly. Sugarcane mulch: every 6–12 months. Gravel/pebble mulch: rarely, only to address settling. Best time to top up: spring (before weeds germinate) and/or autumn (to protect roots before winter). For a refresh, you only need to add 25mm - not the full original depth. The calculator can be used for top-up volume calculations by entering 25mm as your depth.
Wood chip/bark: longest-lasting, neat appearance, good for permanent beds and around trees and shrubs. Straw/sugarcane: excellent for vegetable gardens, breaks down to improve soil, cheap and widely available. Gravel/pebble: permanent, no decomposition, best around succulents and in dry-climate gardens. Compost used as mulch: excellent for fertility but breaks down in weeks. For most ornamental garden beds and low-maintenance gardens, bark or wood chip mulch at 50–75mm is the most practical choice.
Mulch Calculator - How Much Do You Need and What's the Best Way to Buy?
Ordering the wrong amount of mulch is one of the most common garden project mistakes. Too little and you need a second trip to the hardware store (often a different batch, sometimes a different shade). Too much and you're dealing with a heap of material you have nowhere to put. Getting the volume right before you order takes two minutes with this calculator.
Quick example: 3 garden beds - 4m×1.5m, 3m×2m, and 6m×1m - at 50mm (0.05m) depth. Total volume = (4×1.5×0.05) + (3×2×0.05) + (6×1×0.05) = 0.30 + 0.30 + 0.30 = 0.90 m³. At 70L bags: 0.90 ÷ 0.07 = 12.9 13 bags needed. Add 10% buffer = 14 bags.
Mulch Depth Guide - How Deep for Each Application
Recommended Depths
- New garden beds: 50–75mm. Establishes proper weed suppression and moisture retention.
- Annual top-up: 25mm. Refreshes decomposed mulch without over-applying.
- Heavy weed suppression: 75–100mm. High problem areas or pathways.
- Tree and shrub circles: 75mm. Keep 5–10cm clear of trunk/stem.
- Vegetable gardens: 50mm (don't let mulch touch plant stems).
How Much 1 m³ Covers
- At 25mm depth covers 40 m²
- At 50mm depth covers 20 m²
- At 75mm depth covers 13.3 m²
- At 100mm depth covers 10 m²
- 1 m³ ≈ 14 × 70L bags or 10 × 100L bags
- Always add 10% buffer to your calculated volume
Bags vs Bulk - When Each Option Makes More Sense
The crossover point between bags and bulk delivery depends on the price per m³ in your area, but there are practical considerations beyond price:
- Under 1 m³ (up to ~14 bags): Bags are almost always more convenient - no delivery booking, no access requirements, easy to handle one at a time.
- 1–3 m³: Compare carefully. Calculate bag cost (price per bag × bags needed) against bulk delivery (per m³ price × volume + delivery fee). Bulk often wins here but the difference varies.
- Over 3 m³: Bulk almost always wins on price - typically 25–40% cheaper per m³ than bagged equivalents. However, you need good vehicle access to the delivery point, and someone needs to be home to receive it.
- Large landscape jobs: Consider tonne bags (bulk bags) - 800–1000kg each, typically 0.5–0.7 m³ of loose material. Delivered on a pallet, manageable with a small forklift attachment or strong team.
Mulch vs Topsoil vs Compost - Which Do You Actually Need?
These three materials are often confused but serve very different purposes:
- Mulch (bark, wood chips, straw): Goes on top of the soil surface. Suppresses weeds, retains moisture, regulates soil temperature, and improves appearance. Does not significantly add nutrients - it sits on top, not in the growing zone. Best for established beds, tree circles, and pathways.
- Topsoil: The upper layer of mineral soil with organic matter. Used to fill raised beds, level lawn areas, establish new growing areas, or improve thin soil. Mixed into or applied as a growing medium - not a surface covering. Essential when building new garden beds from scratch.
- Compost: Decomposed organic matter - the richest in nutrients of the three. Best dug into existing soil before planting to improve fertility and structure. Can also be used as a surface mulch (breaks down quickly). Ideal for vegetable gardens and newly established beds.
- Gravel/pebble: Decorative and permanent. Does not decompose, so no topping up required. Good for dry gardens, succulents, and areas where organic mulch would mat down. Does not improve soil - it just covers it.
How this calculator works, and where the numbers come from
The Mulch Calculator applies the standard formula for this calculation to the values you enter and updates the result as you type. The calculation itself happens in your browser, and the page explains the method so you can check any result by hand.
Please note: Results are estimates. Add allowance for waste and check product labels and local building codes before you buy or build.
Sources and further reading
Learn more
Read our guide: How Much Paint, Flooring and Concrete Do You Actually Need?