How to measure a radiator

There are many reasons why you might want to measure the size of your radiator. These could include buying a new radiator of the same dimensions, moving your existing one to another wall, or even purchasing a radiator cover.

However, measuring a radiator correctly is slightly more detailed than you might imagine, so in this article we'll explain how to do it so you get the process of measuring your rad right.

The standard unit of radiator measurement is in millimetres (mm) and this is how most radiators advertise the dimensions of their radiators.

Total height and width (mm)

It's always important to know the basic height and width of a radiator, whether you're measuring an existing one or choosing a new one to install.

The wall of the room you're putting a radiator is only going to have a limited amount of space so it's important that you know the total length and width of a radiator that will fit in there.

Measuring the radiator to the highest and widest points will ensure that your radiator will fit in the space you've allocated for it.

Pipe centres (mm)

If you're dealing with a standard radiator that will connect to your conventional, hot water central heating system, it's important you measure the pipe centres of the radiator.

The pipe centre measurement is the distance between the two pipe inlets on your radiator where the rad is connected to your heating system's copper pipework.

If you are replacing an old radiator, then getting a new rad with the same pipe centres measurements will enable you to install your new radiator straight onto the existing pipes without moving them.

Projection (mm)

The projection measurement (aka projection from wall measurement) is basically how far your radiator sticks out from the wall. This measurement can be taken from the wall to front (or furthest point) of the radiator.

The projection measurement becomes particularly important when it comes to putting radiators in narrow or small rooms, like ensuites or hallways.

Choosing a radiator that sticks out a long way from the wall can become a hinderance where space is tight, so in this case, the smaller the projection the better.

Heat output (BTU)

While not a measurement you can take with a tape measure, it's important that you know how much heat your room requires to feel comfortably warm.

The standard way of measuring heat output in the UK is via British Thermal Units (BTUs).

If you have an old radiator, it's difficult to know how many BTUs it is emitting. However, a better way of establishing what heat your room needs is by using a heating calculator.

Once you have put in your room's dimensions to the heating calculator and received a BTU figure for heating the room, you can then search for a new radiator with an appropriate BTU heat output.


The negative consequences of not measuring a radiator properly are:

  • A radiator that doesn't fit the space in your room
  • A radiator that doesn't match up with the pipes coming out of the wall or floor
  • A radiator that sticks out too far from the wall
  • A radiator that doesn't provide enough heat for your room
  • The time and financial cost of rectifying these mistakes

By correctly taking the right measurements for your radiator, you'll help ensure you get the perfect radiator for your room and with minimal complications.

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