Calculating the Inside Diameter of Tubes

CALCULATING THE INSIDE DIAMETER OF TUBES 

To calculate the inside diameter of a tube you just need to take twice the wall thickness from the outside diameter of the tube.

For example:

Tube with a 1” outside diameter with a 14swg (2mm) wall

1” = 25mm

14swg = 2mm

so the calculation would be            

Outside diameter                                         25mm

Minus 2 x wall thickness (2mm x 2mm)       - 4mm

                                                              =     21mm inside diameter

Please find following some SWG (standard wire gauge) sizes and conversions from inches to millimetres for the products we sell on our site.

Standard Wire Gauge

 

SWG

 

Millimetres

 

Inch

 

7

 

4.470

 

0.176

 

10

 

3.251

 

0.128

 

12

 

2.642

 

0.104

 

14

 

2.032

 

0.080

 

16

 

1.626

 

0.064

 

18

 

1.219

 

0.048

Conversion from Millimetres to Inches 

 

Inches (as a fraction)

 

Inches (as a decimal)

 

Millimetres

 

1/8

 

0.1250

 

3.1750

 

1/4

 

0.2500

 

6.3500

 

5/16

 

0.3125

 

7.9375

 

3/8

 

0.3750

 

9.5250

 

1/2

 

0.5000

 

12.7000

 

5/8

 

0.6250

 

15.8750

 

3/4

 

0.7500

 

19.0500

 

7/8

 

0.8750

 

22.2250

 

1

 

1.0000

 

25.4001

 

1 1/8

 

1.1250

 

28.5751

 

1 1/4

 

1.2500

 

31.7501

 

1 3/8

 

1.3750

 

34.9251

 

1 1/2

 

1.5000

 

38.1001

 

1 5/8

 

1.6250

 

41.2751


Galvanised Tube Information

External tube diameter 26.9mm - wall thickness 2.60mm - internal diameter 21.7mm

External tube diameter 33.7mm - wall thickness 3.25mm - internal diameter 27.2mm

External tube diameter 42.4mm - wall thickness 3.25mm - internal diameter 35.9mm

External tube diameter 48.3mm - wall thickness 3.25mm - internal diameter 41.8mm

External tube diameter 60.3mm - wall thickness 3.60mm - internal diameter 53.1mm

Mild Steel Gas Tube Information

External tube diameter 33.7mm – nominal bore 25mm - wall thickness 3.25mm - internal diameter 27.2mm

External tube diameter 42.4mm - nominal bore 32mm - wall thickness 3.25mm - internal diameter 35.9mm

External tube diameter 48.3mm - nominal bore 40mm - wall thickness 3.25mm - internal diameter 41.8mm

All the internal diameters shown are approximate and are intended for general information purposes only as the tolerance on the wall thickness can vary by +/- 10%.

Please note that all figures shown are for guidance only and The Metal Store will not accept any liability for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from the use of these figures or any errors, inaccuracies or omissions shown.