When calculating the number of brick slips required for your project, we recommend factoring in a 10mm grout gap between brick slips as 10mm replicates a mortar joint. The very minimum we advise is a 5mm grout gap due to the +/-2mm tolerance. If you want a smaller grout gap then we recommend you lay all the bricks out prior to fixing.
For the standard brick slips that measure: Length 215mm/Width 65mm/ Depth 15mm base your calculations on 60 brick slips per square metre (This includes a 10mm grout gap)