Size of reel for tether

Hi All

I am new here, and have searched for this info, but have not had any luck so fare.

Anybody know how much a 100m/300ft tether on a reel is. I am asking for diameter (outer and inner) and width of the reel.

Hope somebody can help. Thanks

All the best

You can make a reel many different dimensions to accommodate the same length of tether. You need to do some calculus to reach exact solution. As an approximation, if you have a 300 meter tether, and the width of the reel will accommodate 30 (8mm) tether-widths, then you have 30 separate spirals each 10 m in length. Then if you say that the inner diameter of the reel is 20cm, then you can solve for the outer diameter by constructing a spiral (calculus) using the dimensions of the tether (8mm diameter, 10m long). Here I found an online calculator for the calculus bit: Calculator for Outside Diameter of Roll of Material
Using the above parameters, the calculator tells me the outer diameter will be ~40cm.

By this method, I’ve approximated that a reel approximately 25cm width x 20cm inner diameter x 40cm outer diameter will hold 300m of tether.

This calculator should do the trick. Cable Reel Capacity Calculator - Concept Cables. Remember to give yourself some overhead, as you probably wont have a perfect wind path in practice.

Hi Per,

Jacob is right, all the reel dimensions are interdependent and will vary. In addition, I would recommend an inner diameter of no less than 7 inches to make winding easier both on you and the tether in regard to its flexibility and bend radius. If you take the raw volume of the tether (Lpir^2) I would recommend multiplying this by at least 1.5-1.75 to have a comfortable reel volume which will accommodate the tether even if not wound perfectly.


Hi guys

Thanks for the info, Will run with that info and design a reel.

Looks like I can get around 200 feet on mine in theory. Hmm. I may need a bigger one

Here is a link to a cable reel calculator that I have used at work when building spools and capstan drums. Found it to be on the money all the time.

This calculator will allow you to get a good idea on how many layers you can have and what the projected length is for each layer.