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Size Classification Guide For Pipework And Fittings

Size / Classification Guide For Pipework And Fittings

The following information is provided as a guide only, mainly for customers who are unfamiliar with the sizing and classification of pipework and fittings.
Basically, pipework and fittings of various types are often ‘classed as’ and referred to as one size but will measure slightly different if measured with a tape, ruler or vernier / calliper
We advertise our pipework and fittings as the sizes they are ‘classed as’, just like all other retailers and this is how it should be done, however, we have put together the following guide to help customers determine what pipework they are using or require.
We stock push-fit, solvent weld waste, solvent weld imperial pressure, and solvent weld metric pressure – these different types will not fit each other even if they are classed as the same size, for E.g. 50mm waste will not fit 50mm pressure and so on.
If unclear you can look at the pipe relevant to the fittings you are currently looking at (which will be in the same section on our website) and this will tell you the outside dimension of the pipe, which is also the inside dimension of the fitting required to fit that pipe, *NOTE with the exception of hose pipes and fittings which will be opposite as hose fittings go inside the hose.
Please see below a list of the different types of pipe and fittings showing what they are classed as/ listed as, and also what they actually measure with a tape, ruler, Vernier/calliper


Solvent Weld Waste 

1 ¼” (actual pipe o/d OR fitting i/d 36.4mm)
1 ½” (actual pipe o/d OR fitting i/d 43mm)
2" (actual pipe o/d OR fitting i/d 56mm)
3" (actual pipe o/d OR fitting i/d 82mm)
4" (actual pipe o/d OR fitting i/d 110mm)


Push-Fit Waste

1 ¼”  / 32mm (actual  pipe o/d  34mm)
1 ½” / 40mm (actual pipe o/d 41mm)
2" / 50mm (actual pipe o/d 54mm)


Pressure Imperial

¾” (actual pipe o/d OR fitting i/d 26.7mm)
1” (actual pipe o/d OR fitting i/d 33.4mm)
1 ¼” (actual pipe o/d OR fitting i/d 42.2mm)
1 ½” (actual pipe o/d OR fitting i/d 48.3mm)
2” (actual pipe o/d OR fitting i/d 60.3mm)
3” (actual pipe o/d OR fitting i/d 88.9mm)
4” (actual pipe o/d OR fitting i/d 114.3mm)


Pressure Metric

20mm (actual pipe o/d OR fitting i/d is 20mm)
25mm (actual pipe o/d OR fitting i/d is 25mm)
32mm (actual pipe o/d OR fitting i/d is 32mm)
40mm (actual pipe o/d OR fitting i/d is 40mm)
50mm (actual pipe o/d OR fitting i/d is 50mm)


21.5mm (actual pipe o/d is 21.5mm)

Pond Hose

1/8”  (actual  i/d 4mm)
3/8” (actual  i/d 9mm)
½” (actual i/d 12mm)
¾” (actual i/d 19mm)
1” (actual i/d 25mm)
1 ¼” (actual i/d 32mm)
1 ½” (actual i/d 38mm)
40mm (actual i/d is 40mm)

Bsp Male Thread Outside Diameter

½” Thread (actually measures 20.95mm)

¾” Thread (actually measures 26.44mm)

1” Thread (actually measures 33.25mm)

1 ¼”Thread (actually measures 41.91mm)

1 ½” Thread (actually measures 47.8mm)

2" Thread (actually measures 59.61mm)


Bsp Female Thread Inside Diameter

½” Thread (actually measures 18.63mm)

¾” Thread (actually measures 24.12mm)

1” Thread (actually measures 30.29mm)

1 ¼”Thread (actually measures 38.95mm)

1 ½” Thread (actually measures 45.15mm)

2" Thread (actually measures 56.66mm)


If you need further advice, please call 01922 416284 or email


Litres to gallons

Divide litres by 4.54 = gallons

Gallons to litres

Times gallons by 4.54 = litres


220 gallons is equivalent to 1 ton

Ounces to grams

1oz = 28.350g
1g = 0.035oz
1lb = 0.454kg
1kg = 2.205lbs


1in = 2.540cm
1ft = 0.305m
3.281ft = 1m

How to calculate square pool in gallons

Multiply the length by the width, then multiply that figure by the depth (in feet) then multiply that figure by 6.25 to arrive at the gallons needed

How to calculate round pool in gallons

Multiply half the diameter by half the diameter,
Multiply the answer by the depth of your pool and then multiply that figure by 3.142
That figure is the cubic capacity in feet.
You now multiply that figure by 6.25 for the total gallons in the pool.

How to calculate what size liner you need

Add twice the depth to both the length and the width then add 1ft on both answers
for example: 10ft long by 6ft wide by 2ft deep pool liner would be 15ft by 11ft

Usage of salt

Salt in the pool - ½ ounce per gallon
Salt bath - 3kg per 100 litres for 10 mins max

Usage of zeolite

Zeolite - 2kg per 300 gallons
Recharge in salt for 24 hours every 6 weeks

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