When I was growing up, I associated long charging cables with quality. I assumed the long charging cables were high quality charging cables from actual phone manufacturers and hence the best for charging my phone. 
For a while now, people have been asking me whether the long charging cables (See On Amazon) charge my phone faster than the short ones. At this point I could no longer rely on myths. I had to find a practical and scientific explanation for my theory. Sadly, I was wrong. I’ve been wrong for a long time.
Among other things that affect charging speed, the longer the cable, the longer it takes to charge. Obviously, charging cable speed is also dependent on the quality of wire used and the gauge of the wire. But if all these factors are kept constant, the longer cables take longer to charge.
In our science we know that conductors offer some kind of resistance when electric current is flowing through them. This resistance is dependent on the cross sectional area (gauge) and the length of the conductor. Here’s what their scientific relationship looks like.
From this formula, you can clearly see that when, the cross sectional area (gauge/thickness) of the wire is kept constant, the resistivity inside is directly proportional o the length. Therefore the power output to the device being charged will be less. So scientifically, the length of the cable does affect the charging speed.
A member of forum.xda developers ran a test using three cables of 12, 36 and 72 inches. He noted that the shorter cables had a higher output in amps and hence should charge your phone faster. Here is the graph that was obtained from the experiment.
So, Will the Longer charging Cable Charge Your Phone slower?
It depends. If we compare two cables of the same gauge, then the longer cable will definitely charge slower. The gauge (cross sectional area) also affects charging speed. Cross sectional area is inversely proportional to the resistivity. Therefore the bigger the cross sectional area, the lower the resistivity which translates to faster charging.
If both the long and short cable have outputs equal to or more than the phone takes when charging, then they will charge your gadget at the same speed. For instance; if the long cable’s output is 1.3 Amps and the shorter cable’s output is 1.8 Amps, They’ll charge a 1.2Amps inlet at the same speed.
Answer:
Yes. Cable length does affect charging speed.
