How many cement bags are needed per m³ of concrete?

For standard concrete (250 kg/m³ mix), you need 5 bags of 50 kg per m³. For structural concrete (300 kg/m³), use 6 bags. This calculator uses the typical dosage for each element type.

Why should I add a wastage percentage?

On-site losses from spillage, unusable mixes and level corrections always occur. Adding 5–10 % to your final order ensures you don't run short of material.

What is the difference between mass concrete and reinforced concrete?

Mass concrete has no steel reinforcement and is used for low-load foundations. Reinforced concrete includes steel bars that provide tensile strength, making it suitable for slabs, columns and beams.

Landscape Rock Calculator

Last updated: 2026-06-23

Use the Landscape Rock Calculator to get instant, accurate results. Enter your values below.

Inputs

Dimensions

Area length (m) (m)

Area width (m) (m)

Rock depth (cm) (m)

Area length

Area width

Technical Parameters

Rock density (t/m³)

Rock depth

Rock type

Wastage Allowance (%)

Result

Enter values and press Calculate

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Common Sizes — Click to Fill

Area length (m)	Area width (m)	Rock depth (cm)	Rock type
3 m	2 m	8 cm	1
5 m	3 m	8 cm	1
6 m	4 m	8 cm	1
8 m	5 m	10 cm	1
10 m	8 m	10 cm	2

What is the Landscape Rock Calculator?

Landscape rocks and decorative gravel are sold by weight (tonnes) or volume (m³) depending on the supplier. Ordering by eye always leads to either bare patches or a leftover pile. This calculator converts your area dimensions and desired depth into the exact tonnes or cubic metres to order, using the density of the specific rock type you choose.

You may also find the Mulch Calculator, Paver Calculator, and Sod & Turf Calculator useful.

Who Uses This Calculator?

This tool is used by homeowners landscaping garden beds, landscapers quoting rock supply jobs, and garden centres estimating delivery volumes.

How to Use the Landscape Rock Calculator

Enter your Area length.
Enter your Area width.
Enter your Rock depth.
Enter your Rock type.
Click Calculate to see your results instantly.

Formula

The calculator uses the following formula:

Area = Length × Width; Volume = area × (depth ÷ 100); Tonnes = volume × rock_density

Worked Example

A 8 m × 3 m garden bed with 80 mm depth of river pebbles (density 1.5 t/m³) requires 1.92 m³ of rock, or approximately 2.9 tonnes to order.

Step-by-Step Calculation

Area: 6 m × 4 m = 24 m²
Depth in metres: 8 cm ÷ 100 = 0.08 m
Volume: 24 × 0.08 = 1.92 m³
Crushed granite density ≈ 1.6 t/m³: 1.92 × 1.6 = 3.07 tonnes

Common Mistakes to Avoid

Underestimating depth — decorative rock needs minimum 5-8 cm to suppress weeds
Forgetting to install landscape fabric under the rock
Using volume (m³) pricing when ordering by weight (tonnes) — convert correctly

Pro Tip: Always order 10% extra — rocks settle over time and you'll need top-ups. Specify the exact product name and grade when ordering, since density varies significantly between rock types (crushed granite 1.6 t/m³ vs river pebbles 1.45 t/m³).

Frequently Asked Questions

How deep should landscape rock be?

For weed suppression: 75–100 mm minimum. For decorative effect: 50–75 mm. For pathways: 50 mm. For drainage: 150–200 mm. Deeper layers are more effective at blocking weeds but require significantly more material.

What is the density of common landscape rocks?

Crushed granite: 1.6 t/m³. River pebbles: 1.45–1.5 t/m³. Basalt: 1.6–1.7 t/m³. Decomposed granite (DG): 1.4 t/m³. Limestone: 1.5–1.6 t/m³. Use the correct density for your material to get an accurate weight.

Should I use landscape fabric under decorative rock?

Yes — install woven geofabric before laying rock. It allows water through while blocking weed growth. Avoid plastic sheeting which prevents drainage and kills plant roots. Pin the fabric at edges before covering with rock.

How do I convert between tonnes and cubic metres for rock?

Volume (m³) × density (t/m³) = weight (tonnes). For river pebbles at 1.5 t/m³: 2 m³ × 1.5 = 3 tonnes. Suppliers often quote in one unit — ask for both so you can compare quotes from different suppliers.

How much area does one tonne of landscape rock cover?

One tonne of river pebbles covers approximately 10–12 m² at 50 mm depth, or 5–6 m² at 100 mm depth. For crushed granite, one tonne covers 8–10 m² at 50 mm. Always calculate volume first, then convert to tonnes.

Written and reviewed by the CalcToWork editorial team. Last updated: 2026-06-23.