Calculate the required tube length for key clamps

Calculate tube length for us e with key clamps

Calculating the right tube length

A big part of the questions we're receiving is about calculating the right tube length. In this manual we'll show you as easy as possible how to calculate this. 

1. How far does the tube extend into the clamp?

The extent to which the tube extends into the tube clamp varies depending on the type and diameter of the tube. There is therefore no clear answer to this question.

The required size is often not listed in the table, but it can still be calculated. In the overview below you will see a size chart for a short T-piece. To calculate how far the tube goes into the key clamp, we need to subtract half a tube diameter from distance a.

Example with 42.4 mm: Distance A - ( Ø / 2 ) = 60 - ( 42.4 / 2 ) = 38.8

Please note that minor deviations are possible in stated sizes. Due to the play in a key clamp, this is not a problem for the construction.

Important rule!
In general, tubes in the key clamp should touch each other or should be mounted so that the ends meet. Below you can see some key clamps that have been cut open. It can be seen that the inside is completely open, allowing the tubes to fully touch each other.

Inside of a key clamp inside of a elbow connection cutted key clamp

2. How do I calculate the tube lengths in a frame or construction?

To calculate with tubes, you often already know an internal or external dimension. The outside dimension is the total width of your frame or construction. The inside size is the distance between the tubes.

Do you want from an outside size to an inside size or vice versa? You can easily calculate this. See how you can calculate the different sizes using the image below.

Buislengte berekenen voor steigerbuizen project

Calculate outside dimension (A):
Take the desired internal dimension (B) and add 2x the used tube diameter*.
A = B + (2 x Ø)

Calculate internal size / tube length (B):
Take the desired outside dimension (A) and subtract 2x the used tube diameter*.
B = A - (2x Ø)

Calculate tube length (D):
Take the desired height (C) and subtract 1x the used tube diameter*.
D = C - Ø

*In all cases it is important that you can calculate with a rounded tube diameter. This is easier to calculate and you also take the wall thickness of the key clamp itself into account. In addition, there is sufficient space in tube clamp, so you still have room to adjust.
For 26.9 mm you calculate with 3 cm, for 33.7 with 3.5 cm, for 42.4 with 4.5 cm etc...

Example: Calculate the right tube length for a bar.
The table top of the bar is 150 by 64 cm. Below you want to make a rectangular frame from scaffolding tube 33.7 mm. For the tube length (B) we take the desired outside dimension (D) and subtract 2 times the tube diameter*.
Tube length (W) = D - ( 2 x Ø ) = 150 cm - (2 x 3.5 cm) = 143 cm.
Tube length (W) = D - (2 x Ø) = 64 cm - (2 x 3.5 cm) = 57 cm.

3. How do I calculate the length of a tube between two walls or between floor and ceiling?

If you want to attach a clothes rail or curtain rod between two walls using base plates or place a upright between the floor and ceiling, calculate the correct tube length as follows: 

Calculate tube length for tube between 2 walls

Step 1:
Measure the distance between the two walls or between the floor and ceiling. (distance A)

Step 2:
Based on the tube diameter (Ø) used in the table below, determine how many cm you must subtract from distance A.

By subtracting this margin from the intermediate size, you take the flange thickness of the base plate into account and you have sufficient space to place the tube. Round the calculated tube length down so that you have room for adjustment.

Tube length (B) = intermediate size (A) - F - F

21,3 mm 0,5 cm
26,9 mm
0,5 cm
33,7 mm 1 cm
42,4 mm 1 cm
48,3 mm 1,5 cm
60,3 mm 1,5 cm

4. How do I determine the tube lengths for an advertising frame?

The lengths for tubes of an advertising frame can easily be calculated yourself. For this it is important that you know which tube diameter (Ø) you are going to work with and which type of elastics you want to use. You can calculate the tube length based on the banner size or the desired outside size.

For the calculation and the tension spaces, you can read our blog Everything about advertising frames made of tube.


Do you have any questions after reading this blog? Please contact us. We're happy to help you!

Category:  Guidelines and tips Author: Corbin