Pool Pipe Sizing - Very Confusing

Direct Pool Supplies

A guide here for the pool novice on pool pipe sizing... can be quite confusing...

What size is my pool pipe?
Okay, you want some pipe fittings... you've measured your pipe and it looks close to 50mm diameter, so you go and order 50mm fittings, only to find out they are too large. You think the pool shop has supplied the wrong ones. Well they haven't! Here is the reason...
Why the confusion?
Depending on the class (wall thickness) of the pipe, measurements are all over the place. Originally pipe sizes were based on internal diameters. All fittings were made to glue over the outside of the pipe. As a result, the outside diameter became the critical measurement for pipe sizing. Over time different grades of pipe (and consequently wall thickness) became more popular, so even measuring the internal diameter is inaccurate. The original sizes used and requested have 'stuck' and are now causing confusion, particularly with consumers trying to match pipe & fitting sizes for repairs.
Common pipe sizes used in pools & spas...
The following sizes are for the EXTERNAL diameter of the pipe that goes into the fitting. E.g... if you want to purchase an elbow, and the pipe diameter that the elbow needs to go onto is approximately 48mm, you need to purchase a 40mm elbow. From the below chart, 40mm & 50mm are the most common in swimming pools.  
The pipe/fitting size you need to order
Actual size of the pipe
1/2" / 15mm
3/4" / 20mm
1" / 25mm
1.5" / 40mm
2" / 50mm
2.5" / 65mm

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