In a one-third offset, slabs are laid in rows and each row is shifted by a third of the slab length against the one before. After three rows the pattern repeats. This template shows 600 × 300 mm slabs (about 24 × 12 in), a popular size for modern patios. In PatioPlanner the pattern is called Stretcher bond.
Why a third and not half?
Large concrete slabs are rarely perfectly flat. A slight bow along the length is enough: in a half offset, the highest point of one slab, its middle, lines up with the ends of the neighbouring slabs. That leaves a lip you can trip over and where water collects.
With a one-third offset the height difference at that spot is smaller. Many manufacturers of large-format slabs specify an offset of a third at most for that reason. Check the installation guide for your slab before you commit.
Slabs per square metre
A three-row repeat measures 600 × 900 mm and holds three slabs. That is 5.6 slabs per m² (about 0.5 per sq ft) without joints, or roughly 139 slabs for a 25 m² patio before waste.
With large slabs, every cut costs more than with small pavers. The slab is pricier, the cut takes longer, and a small offcut is often useless. That makes the planner’s optimizer especially worthwhile here.
Recreate the template in PatioPlanner
The “Open template in planner” button loads the standard rectangular paver with the stretcher bond. You set the slab size yourself:
- Under “Choose the brick type”, pick “Custom dimensions” and enter 600 × 300 mm. Switch the measurement unit to inches if you measured in imperial. Then click “Apply pattern” again. The pattern takes the new size and keeps the one-third offset.
- Decide which way the rows run. At a rotation angle of 0° they run across the drawing, at 90° from top to bottom. Rows running away from the viewer make a patio look deeper, rows running across make it look wider.
- Pick the start corner. With slabs, the full row belongs against the house or along the edge you see from the living room.
- Use the optimizer. “Joint + area combined” searches for the best mix of joint width and surface size. If the patio is still on paper, a few centimetres often save a whole row of cut slabs.
- Check the shopping list. It shows full slabs and slabs to cut separately, plus grit for the bedding and crushed stone for the base.
Tips for laying
- Do not butt slabs tight without a joint. Under load the edges chip. Use the joint width your manufacturer specifies.
- Run a string line for each row and mark the 200 mm offset on the first slab. That keeps the third consistent across the surface.
- Large slabs need a very even bed. Screed the grit carefully and tap slabs down with a rubber mallet, not with a plate compactor that has no protective pad.
FAQ
How many 600 × 300 mm slabs do I need per m²?
In theory 5.6 per m² without joints. Joints bring it down slightly, waste brings it up. The shopping list in the planner calculates both for your surface.
One-third offset or half offset?
With small pavers it hardly matters. With slabs from about 600 mm long, the one-third offset is the safe choice because bowing is less visible. The classic half offset is covered in the running bond calculator.
Does the template work with other sizes?
Yes. Enter any rectangular size under “Custom dimensions”, such as 800 × 400 mm or 900 × 450 mm. The offset always stays one third of the length.