Thunderbolt 3 cable length myth?

Is it true that thunderbolt 3 cables have to be short to maintain full function? I read somewhere that a longer TB3 cables wouldn’t be able to maintain the full transfer speeds. I’ve got 2 of the @AnkerOfficial TB3 at 0.5m (19.7in) that work great but have also seen other (non anker) cables at a 2m length offering full charging and data transfer speeds and obviously a hefty price tag! Can anybody add any truth or maybe debunk the myth?

Ps. Sorry if this has been covered before.

Not specific to Thunderbolt but cables in general.


Resistance is roughly linear on cable length. So say a cable of a given thickness, if you double the length you have double I-squared so increase current by 40%, or put it another way, you lose power with cable length.

You lose voltage too, so 20V in becomes less and less with cable length.

To compensate you have to make cables thicker if longer, so a cable twice as long must also be twice the cross section so you need 4 times as much copper in the wire.

So you either:

  • pay a lot more the longer wire for the more copper, or
  • find speeds drop, power drops, or
  • use shorter cables.

So you need to bring the AC power as close as possible, with Anker that would be Powerstrip or a corded desk charger, to make the USB cables shorter.

Thanks for taking the time with to reply. Thats really useful to know. To be honest, I haven’t got a massive need for a 2m TB3 cable but the thought was nice.