Kerb & Edging Concrete Calculator
Estimate concrete for the bed and supporting haunch, including waste, bags and optional material cost.
- Waste allowance: 10%
- Haunch shape: triangular section on both sides.
- Whole bags are rounded up using 12.5 L mixed yield per bag.
Use this kerb edging concrete calculator to estimate how much concrete you need for a bedding layer and optional side haunches. It is designed for garden edging, path edging, driveway kerbs and similar linear installations where concrete is placed beneath and beside each unit.
Enter one or more run lengths, then add the bed width and depth. You can include a triangular haunch on one side, both sides or neither side. The calculator adds your chosen wastage allowance and shows the final concrete volume, a run-by-run breakdown and an optional cost estimate.
You can work in metric units using metres and millimetres, or switch to imperial units using feet and inches. Results are displayed in cubic metres and litres for metric calculations, or cubic yards and cubic feet for imperial calculations.
PRO TIP: Measure the actual trench and proposed concrete profile rather than relying only on nominal kerb dimensions. Ground conditions, excavation tolerances and uneven sub-bases can all increase the amount of concrete used. For long runs, divide the work into logical sections and enter each section separately so that the run breakdown can help with batching and sequencing.
How to use this kerb & Edging concrete calculator
Choose your units
Select metric for run lengths in metres and smaller dimensions in millimetres. Select imperial for run lengths in feet and smaller dimensions in inches. When you switch units, the calculator converts the values already entered rather than simply relabelling them.
Enter each kerb or edging run
Enter the full installed length of the first run. Use the add-run option for separate sections, such as two sides of a path, several garden borders or different driveway edges. Every run must have a positive length. The calculator totals all runs before calculating the concrete requirement.
Enter the concrete bed dimensions
The bed width is the width of the rectangular concrete layer beneath the kerb or edging. The bed depth is the thickness of that layer. Measure the intended concrete dimensions rather than the dimensions of the kerb itself.
Add side haunching
Choose no sides, one side or both sides. When haunching is selected, enter the width and height of each haunch. The calculator treats each haunch as a triangular section, which reflects a typical sloping support rather than a full rectangular block.
Select the supply method
Choose ready-mix when concrete will be ordered by volume. You can enter a price per cubic metre in metric mode or per cubic yard in imperial mode. Choose bags when using pre-mixed concrete. Standard presets are provided for 20 kg, 25 kg and 40 kg bags, with assumed yields of 10, 12.5 and 20 litres respectively. A custom bag yield can also be entered.
Set wastage and cost
Enter a wastage allowance from 0% to 50%. The default is 10%. Optional price fields can be left blank when you only need quantities. Ready-mix cost is based on the final volume after wastage. Bag cost is based on the number of whole bags required, rounded up.
results explanation
Total length
The combined length of every run entered. This is the length used for both the bed and haunch calculations.
Bed volume
The volume of the rectangular bedding layer beneath the full kerb or edging length.
Haunch volume
The combined volume of all selected triangular side haunches. This is zero when no haunching is selected.
Net volume
The bed volume plus the haunch volume before wastage.
Waste volume
The extra amount added using your chosen wastage percentage.
Final volume
The total concrete requirement after wastage. In metric mode this is shown in cubic metres and litres. In imperial mode it is shown in cubic yards and cubic feet.
Whole bags
For bagged concrete, the calculator divides the final litres by the selected bag yield and rounds up to the next whole bag. This avoids showing an impractical fraction of a bag.
Estimated cost
For ready-mix, cost is the final volume multiplied by the entered price per cubic metre or cubic yard. For bagged concrete, cost is the rounded-up whole-bag quantity multiplied by the cost per bag.
Run breakdown
Each run is listed separately with its combined bed and haunch volume. This is useful when planning phased work or checking how much concrete is needed for different areas.
How the Maths Works
The calculator converts every measurement to metres internally so that all concrete volumes can be calculated in cubic metres. Imperial measurements are converted using 1 foot = 0.3048 metres and 1 inch = 25.4 millimetres.
Concrete bed
The bedding layer is treated as a rectangular prism:
Bed volume = total length × bed width × bed depth
Concrete haunch
Each side haunch is treated as a triangular prism. The triangular cross-sectional area is half the haunch width multiplied by the haunch height:
Haunch volume = total length × number of sides × 0.5 × haunch width × haunch height
Final concrete volume
The bed and haunch volumes are added to give the net volume. Wastage is then added:
Final volume = net volume × (1 + wastage percentage ÷ 100)
Bag quantity
The final cubic metres are converted to litres using 1 cubic metre = 1,000 litres. The required number of bags is then rounded up:
Whole bags = final litres ÷ litres yielded per bag, rounded up
Displayed imperial volumes
For imperial results, cubic metres are converted using approximately 1 cubic metre = 1.30795 cubic yards or 35.3147 cubic feet.
Common Mistakes to Avoid
- Entering the kerb width instead of the full concrete bed width.
- Forgetting that a haunch on both sides doubles the triangular haunch volume.
- Mixing metres with millimetres, or feet with inches, in the wrong fields.
- Using the bag weight as the bag yield. The calculator needs litres of mixed concrete produced per bag.
- Leaving out bends, returns, end sections or short connecting runs.
- Using no wastage allowance where the trench is uneven, or measurements are approximate.
- Assuming the calculated ready-mix volume will match a supplier’s minimum order or delivery policy.
- Rounding bag quantities down instead of using the whole-bag result.
faqs
How much concrete do I need under kerb edging?
The amount depends on the total run length and the width and depth of the bedding layer. It increases further when one or two side haunches are added. Enter the intended concrete dimensions into the calculator to estimate the volume.
Should kerbs and edging be haunched on one side or both sides?
That depends on the edging type, loading, ground conditions and installation detail. Some light garden edging may need less restraint than driveway or traffic-adjacent kerbs. Follow the product or project specification and seek professional advice where the edging is structural or load-bearing.
What wastage allowance should I use?
The calculator defaults to 10%, which is a practical starting point for many small jobs. A more regular excavation may need less, while irregular trenches, spillages, hand mixing or uncertain measurements may justify more. The calculator accepts 0% to 50%.
Is bagged concrete or ready-mix better for kerb edging?
Bagged concrete can suit small or staged jobs because it is easy to buy in whole bags. Ready-mix can be more practical for larger continuous runs, but delivery access, minimum order quantities and placing time should be checked with the supplier.
How do I estimate the cost of ready-mix concrete?
Enter the supplier price per cubic metre when using metric units, or per cubic yard when using imperial units. The calculator multiplies that rate by the final volume after wastage. Delivery, part-load, waiting-time, pump and access charges are not included.
How are bag quantities calculated?
The final concrete volume is converted to litres and divided by the stated litres yielded per bag. The result is rounded up to a whole bag. Presets use 10 litres for 20 kg bags, 12.5 litres for 25 kg bags and 20 litres for 40 kg bags, but you can enter a custom yield from the manufacturer’s information.
Does this calculator confirm the correct foundation or kerb specification?
No. It estimates concrete quantity from the dimensions you provide. It does not design the installation or confirm suitability for loading, drainage, ground conditions, product requirements or regulatory compliance.
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disclaimer
This calculator is an estimating tool based on the measurements and options entered. Actual concrete use may vary because of excavation tolerances, uneven ground, compaction, settlement, spillages, batching variation and the final shape of the bed or haunch.
Bag yields are assumptions taken directly from the supplied calculator logic: 20 kg = 10 litres, 25 kg = 12.5 litres and 40 kg = 20 litres. Manufacturer yields can differ, so check the packaging or technical data and use the custom yield option where necessary.
Cost estimates cover only the entered concrete rate or bag price. They do not include delivery charges, minimum-load charges, part-load fees, pumps, labour, plant, reinforcement, sub-base materials, excavation, disposal, formwork or VAT unless those costs are already included in the price entered.
The calculator does not provide structural design advice. Installation details should follow the kerb or edging manufacturer’s instructions and the project specification. Work near highways, drainage, services, retaining structures or load-bearing areas may require a competent contractor, engineer, utility checks, permissions or professional sign-off.
Use appropriate personal protective equipment when handling cement and concrete. Avoid skin and eye contact, control dust when opening or mixing bags, and follow the product safety information. Fresh concrete and cement-based materials can cause serious burns.