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How to Calculate Wire Rope and Cable Stretch



When designing cable or wire rope systems, the amount of stretch that will occur when a force is applied is an important consideration. Keep the following in mind when you do your calculations:

There are two forms of stretch in cable and wire rope: Structural Stretch and Elastic Stretch.

Structural Stretch

Structural Stretch is the lengthening of the lay in the construction of cable and wire rope as the individual wires adjust under load. Structural Stretch in Loos & Co., Inc. products is less than 1% of the total cable length. This form of stretch can be completely removed by applying a cable or wire rope prestretching operation prior to shipment.

Elastic Stretch

Elastic Stretch is the actual physical elongation of the individual wires under load. The elastic stretch can be calculated by using the following formula*:

E = (W x G) / D2


E = Elastic Stretch, as a % of Length**

W = Weight of Load, in pounds

D = Diameter of cable, in inches

G = See Chart Below

Cable/Wire Rope

"G" Factor

Cable/Wire Rope

"G" Factor 

1x7 302/304 SST


1x7 Galvanized


1x19 302/304 SST


1x19 Galvanized


7x7 302/304 SST


7x7 Galvanized


7x19 302/304 SST


7x19 Galvanized


6x19 302/304 SST IWRC    


6x19 Galvanized IWRC      


6x25 302/304 SST IWRC


6x25 Galvanized IWRC


19x7 302/304 SST


19x7 Galvanized


*Elastic Stretch derived from this formula is an approximation.

**Remember to keep your units of measure constant. The length of your cable must be calculated in inches to correspond with the diameter measurement, also in inches

For more information, and to download a free stretch calculator from our website, contact a product manager or visit our technical information page.


A lot of great information here
Posted @ Friday, July 02, 2010 2:15 PM by Brad Herlihy
I have two metal (State specs) galvanized guard rail post 5'-9"" long that I cemented 3 feet into the ground. There is a steel (Zinc) coated 1'' thick cable wire attached to both ends. It spans 35 feet across a private road. The guard rail post have pre-drilled holes that the cable ends just fit through. On one end post, the wire is held tight with two-3/4'' wire rope cable clips, & on the other end is where I need to make this cable with enough tension to stay up & across the road. This 1'' cable rope wire is very heavy stuff. So! with that being said, I need a turn-buckle adapter to fit this 1'' diameter wire cable so that I can remove the cable from the private road at times. & also run a lock too it, to lock it up when not in use. I can't do the conventional style of looping the cable ends & tying them with two more wire rope clips & then installing two eye bolts to attach this. This 1'' wire cable has very little bend & give to it. What can you do for me ? I'm up for suggestions... 
Thanks for your time, 
Mike Lashinsky 
602 Pittsburgh Street 
Scottdale, Pennsylvania 
(724) 887 - 5870
Posted @ Wednesday, December 01, 2010 5:39 PM by Mike Lashinsky
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Posted @ Monday, August 27, 2012 5:42 AM by Cabs and Car in jodhpur
I have been using the resonant frequency of a stretched cable to gauge the tension. I can practically measure the frequency to about 1 Hz which should convert to tension with an accuracy of about 10 lbs. Will a tension gauge provide a better measurement and under what circumstances?
Posted @ Monday, November 19, 2012 10:53 PM by doc dough
Doc –  
Thanks for the question. It looks like you know your aircraft cable tension details!  
Our Digital Cable Tensiometer’s precision and accuracy is dependent on your application’s cable size and tension range. Our Digital Cable Tensiometer is capable of registering tensions with the tightest tolerances being ±4 lbs. These tolerances have been outlined, and you can find this information table on our Digital Cable Tensiometer Tech Specs page ( ). Hope this answers your question, and if not, feel free to contact us again. Thanks!  
Posted @ Monday, November 26, 2012 12:13 PM by Patrick Bagshaw
Dear All  
I want to know how to calculat elasticity of polypropylene rope 
Plz provide me if possible. 
N K Ojha
Posted @ Friday, January 18, 2013 5:23 AM by Navneet K Ojha
Dear All  
Plz calculate elasticity of polypropelene ropo if dia= 6", wt/meter 1.050 Kgs. 
How can I calculate it, plz provide me formula step by step. 
Posted @ Friday, January 18, 2013 5:27 AM by Navneet K Ojha
Thanks for your question, Navneet. As you can see from our Blog, the HotWire discusses the performance characteristics of the materials that Loos & Co., Inc. manufactures, primarily stainless steel and galvanized aircraft cables. If you would like to learn more about the stretch of plastic ropes, you would be best served by contacting a plastic rope manufacturer or distributor. Thanks again for your interest and I wish you the best on your search.
Posted @ Friday, January 18, 2013 8:35 AM by Robert Davis
I am trying to find out what would be the difference in the size of cable new to a cable that has been excessivly used. Is there an equation to figure out size due to wear?
Posted @ Tuesday, April 30, 2013 11:32 AM by Kelly Gee
Unfortunately, no equation to determine wear and/or remaining service life exists. Routine inspection for broken or worn wires is the best method to insure that the cable you are using is still fit for service. If you have any questions, don't hesitate to call us and review with a Loosco Product Manager.
Posted @ Monday, May 06, 2013 7:26 AM by Robert Davis
Situation: Installed on my sailboat two wires, each 37 ft long, size 5/16, 19 strand, 316 stainless steel. {These are shrouds, one each side of the mast from deck to approx 3/4 of the way up. There are 3 other shrouds each side of the mast.} 
Tension on the new wires was set to 10% using Loos gauge. After 24 hrs, I've seen approx 1 inch of stretch. So I re-tensioned them to 10%. 
How many total inches of stretch should I expect? {approx) 
If I get another two inches of stretch - I'll actually be happy. Otherwise, I might have really cut them too short. Oops. 
Any idea if they will stretch much more? Thanks! 
Posted @ Sunday, February 09, 2014 10:05 PM by James Joseph
It sounds like you're removing the structural strecth from the cable -- which will be well below 1% of the overall length on a 1x19 cable. I would not expect that your cable will stretch much more.
Posted @ Monday, February 10, 2014 7:50 PM by Robert Davis
Nice Post!!
Posted @ Monday, March 03, 2014 4:11 AM by Alisha Joe
I found this post very useful. I learned how to calculate Wire Rope and Cable Stretch.
Posted @ Tuesday, April 15, 2014 6:41 AM by Anup Gupta
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Posted @ Wednesday, August 27, 2014 7:24 AM by Bridal saree
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