Homeowner Professional

Once the number of square meters of the roof is known, the next step is to calculate how many slates you will need

How many slates per square metre (m2)?

This table shows the required number of slates per square metre for effective coverage.

The number of roof slates that are needed depends on the slate size and the lap in mm.

The values shown in the Slate Coverage chart above are calculated using nominal sizes and incorporate a 5mm jointing gap. We recommend the addition of at least 5% wastage allowance.
Quantity of Slates
Slate SizeLap mm
(Nominal) mm5065758090100110115120130140150
600 x 30012.112.512.712.813.113.313.613.713.914.214.514.8
500 x 30014.815.315.715.916.316.717.117.317.518.018.519.0
500 x 25017.818.418.819.019.520.020.520.821.021.622.2
450 x 30016.717.317.818.018.519.019.619.920.220.821.5
400 x 25020.220.821.321.622.222.923.523.924.225.025.8
450 x 23021.722.623.223.524.224.825.626.026.327.228.1
400 x 30019.019.920.520.821.522.223.023.423.8
400 x 25022.923.924.625.025.826.727.628.128.6
400 x 20028.629.930.831.332.333.334.535.135.7
350 x 30022.223.424.224.725.626.727.8
350 x 25026.728.129.129.630.832.033.3
350 x 20033.335.136.437.038.540.041.7
320 x 22033.735.737.137.939.541.343.3
320 x 18041.243.645.446.348.350.553.0
300 x 20040.042.644.445.547.650.0
300 x 15053.356.759.360.663.566.7

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