How the Edging Kerb Calculator Works

Enter your total run length, choose your kerb or edging type and calculator divides by unit length, adds wastage and rounds up to whole units. It then works out the bedding concrete from your run at standard bed depth and haunching concrete from triangular profile behind units.

The key number for full size kerbs, standard British Standard kerbs are 915mm long, so a run in metres divided by 0.915 gives the unit count. A 20 metre driveway edge needs 22 kerbs before wastage or 24 with 5 percent added for cuts and odd casualty. Garden edgings typically come in 600mm and 915mm lengths and follow the same maths.

Kerb and Edging Types Explained

The names describe the profile and profile matches the job:

• Half battered (HB2): the classic road kerb with a sloped top face, 125 x 255mm, used where vehicles meet a raised footway
• Bullnosed (BN): a rounded top edge, gentler on tyres, common on driveways and crossings
• Splayed (SP): an angled face that deflects wheels, used on higher speed roads
• Flat top edging (EF): the 50 x 150mm flush edging strip used to restrain paths and block paving
• Round top and decorative edgings: garden profiles for lawns, borders and paths, typically £7 to £20 per linear metre

Two details save redesigns later. Transition kerbs are needed wherever kerb type changes and dropped kerb runs at driveways use dedicated dropper units to step height down, with a 6 to 13mm upstand at vehicle crossings.

The Concrete Does the Real Work

A kerb is only as strong as its bed and haunch, because units themselves just sit there. The bed is a semi dry concrete around ST1 or C7.5 strength, mixed at roughly 6 parts 10mm gravel, 3 parts sharp sand and 1 part cement, laid at least 100mm thick. The mix should be stiff enough to mould into a ball, since a sloppy bed lets units float off level as you tap them down.

Haunching is concrete wedge placed behind units after alignment is checked and it is what resists a car wheel striking the kerb. Bring it up to around two thirds of unit height, at least 75mm wide for paths, 100mm for driveways and up to 150mm for heavier duty, compacted tight with back of a trowel. Let it harden before laying the adjacent paving or the units will move.

As a planning figure, allow roughly 0.03 cubic metres of concrete per linear metre for a garden edging bed and haunch combined and around double that for full size road kerbs.

Laying Tips From the Trade

Set a string line at finished level and lay to it, tapping each unit down with a rubber maul and checking level across the unit as well as along the run. Joints are laid at 2 to 4mm dry or 5 to 10mm mortared, never butt units tight together because concrete against concrete chips at arrises. On curves, work to string with a spirit level back check and expect more cuts, which is where wastage allowance goes. Like paving blocks, kerbs vary subtly between batches, so draw from multiple packs as you lay on any visible run.

Worked Example

A 15m driveway edge in bullnosed kerbs with a 3m dropped crossing:

• Full kerbs: 12m ÷ 0.915 = 14 units, plus 5 percent = 15
• Dropped crossing: 2 dropper kerbs plus 3 centre dropped units
• Bedding and haunching concrete: 15m at roughly 0.05 m³ per metre = 0.75 m³
• That is around 2 bulk bags of ballast and 9 bags of cement mixed on site

Order specials with standard units, since droppers and radius kerbs often carry longer lead times than stock straights.