Before buying an under-floor heating system for your living room, kitchen or bathroom, it's pretty important you know the size of the area that needs covering.
I've given some examples below to help you measure the area correctly, this will hopefully give you a good indication of what size heating mats you need.
Measuring your kitchen for an under-floor heating system To measure correctly for heating in your kitchen:

1. Measure the length and width of your kitchen.
   A typical example could be 3.
   5m long and 3.
   5m wide.
   
2. Then multiply these measurements to give you the total area.
   Following from the above example, 3.
   5 x 3.
   5 = 12.
   25m2
3. To ensure the underfloor heating mat fits correctly and that you are only going to heat the area you require, you will now need to remove the total area of any kitchen units or other items which would be on top of the mat.
   Continuing with the example above, a kitchen unit could be 0.
   6m wide and if the units were along 3.
   5m of wall in the kitchen, this would be 0.
   6m x 3.
   5m = 2.
   1m2.
   You should take this amount and subtract it from your total kitchen floor area.
   
4. The total area which you need to cover is 12.
   25m2 - 2.
   1m2 = 10.
   15m2.
   
5. Most under-floor heating mats are available in multiples of 1 square meter, so covering a 10.
   15m2 surface area would require 10 x 1.
   0m2 mats or variations of larger sized mats.
   

How to measure your bathroom for an under-floor heating system To correctly measure the space in your bathroom you want heated you should:

1. Measure the length and width of your bathroom.
   An example would be 3m long and 2.
   5m wide.
   
2. Then multiply your measurements to get your total area.
   Following from the above example, 3.
   0 x 2.
   5 = 7.
   50m2
3. To ensure the under-floor heating mat fits and that you are only going to heat the area you require, you will now need to remove the total area of any fixtures and bathroom units or other items which could potentially be on top of the mat.
   Continuing on from the example above, if you have a bath, the typical size of this would be 70cm wide and 170cm long.
   You will need to remove the square meterage if you don't have a bath in yet.
   The square meterage of the bath area would be 70cm x 170cm = 1.
   19m2
4. The total area which you need to cover is 7.
   50m2 - 1.
   19m2 = 6.
   31m2.
   

What if the mats available don't suit my requirements? Most under-floor heating mats can't be cut to size but will usually fit the majority of the area you want heated.
If you have an unusual shaped area to heat then maybe the matted system isn't the right choice for you.
Instead you may find that the more versatile, self-regulating cable system, may be more suited to your needs.