# Estimating Cable Length on a Reel

I have been searching all areas of the internet to try and find a reliable formula for estimating cable length on a reel,

I'm trying to create a faster and more reliable way to estimate cable to enhance the speed of our Stock Take.

So far I have found one formula that makes sense to an extent but falls short on the layers calculation (step 6-8) this can be found here: http://www.ehow.co.uk/how_7464814_estimate-cable-reel.html

The reel sizes and cable diameter change per reel.

I used the guide above to measure a single wrap around of cat 5e, 4 layers thick and the results were out by at least 200mm, (77% inaccuracy)

Here are the measurements i recorded;

Center of the reel diameter : 57.5mm
Cable diameter : 4.3mm
Width of the Reel : 4.3mm (single layer of the cat 5e),
Flange Used : 17.2mm

Total Length : 756mm - Using the formula below

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Formula for working out the 4 layers is:
Using the Example Above
Layer 1 = (4.3*2)3.14
Layer 2 = (4.3*2+4.3)3.14
Layer 3 = (4.3*2+4.3+4.3*2)3.14
Layer 4 = (4.3*2+4.3+4.3*3)3.14

Can anyone see where i am going wrong?

I Manually counted the length and it was 980mm

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I noticed a trend in the increase of length per layer which was 30mm, is this relevant to factor in at any point in the guide?

I am by no means a Math Professional, so my mind is slightly boggled!

Any help at all would be appreciated.

Thank you

• anyone have any idea on a standard formula for calculating cable length on a drum/reel? – Matthew Dec 8 '15 at 9:51
• I'm voting to close this question because it's old; I suspect the OP no longer needs an answer. – Ethan Bolker Oct 15 '18 at 14:11
• what is "center of the reel diameter" ? the diameter of the reel without cable ? – G Cab Aug 17 at 19:18

$$Cable \space length = {[1] - [2] \over [3]}$$