Selecting the Correct Cable To select the correct cable you need to know a few things, Free Heated Floor Area? Primary or Secondary Heating? Once you know the free floor area you can move on to selecting the correct cable for yourself. Each cable has a minimum and maximum square metres, these are what the cable would cover at 100w/m2 being the smallest measurement up to 200w/m2 being the highest measurement. Size Power Cable Length Coverage at 100W/m2 Coverage at 150W/m2 Coverage at 200W/m2 0.8-1.5m2 150 12.5 1.5m2 1m2 0.8m2 1.1-2.3m2 225 18.75 2.3m2 1.5m2 1.1m2 1.5-3.0m2 300 25 3.0m2 2m2 1.5m2 1.9-3.8m2 375 31.25 3.8m2 2.5m2 1.9m2 2.3-4.5m2 450 37.5 4.5m2 3m2 2.3m2 2.6-5.3m2 525 43.75 5.3m2 3.5m2 2.6m2 3.0-6.0m2 600 50 6.0m2 4m2 3.0m2 3.4-6.8m2 675 56.25 6.8m2 4.5m2 3.4m2 3.8-7.5m2 750 62.5 7.5m2 5m2 3.8m2 4.5-9.0m2 900 75 9.0m2 6m2 4.