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Radiator Size Finder

Radiator Size Finder – Choose the Perfect Radiator for Your Space

Welcome to our Radiator Size Finder — your first step towards selecting the right radiator for your room, style, and heating needs. We understand that when it comes to heating, size matters: the correct height, width, column count, and location can make all the difference in both performance and aesthetics.

As heating specialists, Radiators 4u don't just offer standard sizes; we provide one of the UK’s most extensive collections of designer, cast iron, electric, and high-efficiency aluminum radiators. We pride ourselves on offering free UK delivery on a vast range of products, ensuring your perfect match arrives quickly and safely. So, whether you’re looking for a specific colour finish to match your decor or a high-output solution for a drafty extension, our selection is curated for both durability and style.

Using this page, you’ll find simple guidance and interactive tools to help you calculate the optimal radiator size. Whether it’s a cosy bedroom, a grand bay window, or a modern bathroom, our size-finder helps you avoid guesswork and prevents costly "oversize" or "undersize" errors.

If you’d rather speak to someone, our expert technical advisors are ready to guide you through the selection process, helping you navigate technical specs and finish options for a truly bespoke heating solution.

How Does it Work? - Just tell us the size you need – we’ll find the best match. Enter the measurements of your existing radiator or the space you want to fill. We’ll search our full range to find the closest fit. If we have the exact size — great! If not, we’ll show you the nearest options along with any telescopic adaptors you might need to make the installation seamless.

Example Matches:

Perfect Match
perfect match

This radiator exactly matches the space you are looking for. No adaptors are required.

Height Match
height match

This radiator matches the height perfectly, however it is 40mm too narrow, you can use 2x 20mm adaptors to fill the space perfectly.

Nearest Match
close match

This radiator has the closest height match but is not exact. There is a width diffrence of -54mm so we recommend using 2x telescopic adaptors set to 27mm each. Using 2 adaptors allow you centralise your radiator between the valves.

 
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FREQUENTLY ASKED QUESTIONS

Questions from our beloved customers

  • How do I measure radiator size?
    Height: Measure from the very top of the radiator to the bottom. Width: Measure the radiator from left to right (excluding valves). Pipe Centres: Measure the distance between the centres of the two water pipes. Wall to Centre: Measure from the wall to the middle of the radiator pipe to ensure the depth is correct.
  • I have a bay window; how should I use the Radiator Size Finder?
    Because bay windows consist of multiple angled sections, you shouldn’t measure the total curve as one unit. Instead, measure each flat wall segment individually. Use the Size Finder to find small, separate radiators for each section, or contact us for further assistance.
  • Should I measure my radiator with or without the valves?
    When using the Size Finder to replace a unit, measure the radiator body only (from end to end). However, when checking if a new radiator will fit into a fixed gap between existing pipes, remember that valves typically add about 60mm–80mm to the total width.
  • What size radiator do I need?
    The "size" you need is determined by two factors: the physical dimensions of your wall space and the heat output (BTUs) required to warm the room. You should first calculate your required BTUs, then use the Size Finder to filter for radiators that meet that output within your available height and width limits.
  • What are BTUs?
    BTU stands for British Thermal Unit, which is the standard measurement of heat output. The higher the BTU rating of a radiator, the more heat it will emit into the room.
  • How many BTUs do I need to heat my room?
    This depends on the room’s volume (Height x Width x Length), the number of windows, and the insulation of your walls. For a precise calculation, we recommend using our BTU Calculator.
  • What are "Telescopic Adaptors" and when do I need them?
    Telescopic adaptors are adjustable fittings that allow you to connect a new radiator to existing pipework if the new unit is slightly narrower than the old one. They "stretch" to bridge the gap, saving you from having to drain your system and move the pipes.
  • Does the material of the radiator affect the size I need?
    Yes. For example, aluminum radiators have very high outputs, meaning you can often use a smaller unit to get the same heat as a larger steel one. Conversely, cast iron is denser and heats up more slowly, often requiring a slightly larger physical presence to achieve the same immediate "blast" of heat - however it stays warm for much longer after the heating is turned off.
  • Will a vertical radiator give me the same heat as a horizontal one?
    Absolutely. Heat output is about surface area and efficiency, not orientation. A vertical radiator with a 5,000 BTU rating will heat a room exactly the same as a horizontal radiator with a 5,000 BTU rating.
  • Is it better to have one large radiator or two smaller ones?
    In large or "L-shaped" rooms, two smaller radiators are often superior. Placing them on opposite sides of the room creates more even heat distribution and eliminates "cold spots" that can occur if a single large radiator is struggling to push heat to the far corners of the space.
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