Does cable length affect charging speed?

When we are charging our smartphones and other gadgets, its obvious that most of us would want the smartphone or gadget to charge to 100% as fast as possible. Thanks to so many Quick Charge/Fast Charge technologies, however, 10-15 minutes of charge can supply hours of usage time. 

Apart from that, there are still some other factors that can slow down your smartphone’s charging speed. These factors include the quality of your cable, the gauge/thickness of the wires insides your charging cable, amperage of power adapter & cable and some other factors. Another important factor that affects the smartphone charging speed of a smartphone which people often overlook is the length of the cable being used to charge the smartphone.

So Does cable length affect charging speed? yes; the length of your USB cable could either increase or decrease the charging speed (and time) of your smartphone. Let me explain below.

Relationship between cable length & charging speed

Given that two cables are made of the same wires and have equal thickness, why would the shorter cable charge faster than the longer cable? Science.

The relationship between the length of a cable and the speed at which it supplies power to your smartphone battery can be explained by the formula (of resistivity) in the image below.

Electrical conductors (wires) in your charging cables offer some level of resistance (opposition to the flow of electrical current) when electricity is being passed through them. The level of resistance they offer is dependent on two factors (as expressed in the formula above):
The gauge/thickness/cross-sectional area of the wire, and
The length of the wire/conductor

Using the formula above, let’s assume two cables (A & B) have equal gauge/thickness of 1mm but are 6mm and 4mm long respectively. Let’s calculate their resistance.

Cable A’s resistance is 6 (i.e. 6mm/1mm) while Cable B’s resistance is 4 (i.e. 4mm/1mm). As the result shows, the longer a wire is, the greater the resistance and consequently, the lesser electric current (in amperes) it is able to supply to your device.

This is, of course, a theoretical explanation. Let me walk you through the results of someone who has tried, tested, experimented and confirmed that the length of your USB cable indeed has an impact on the speed at which your smartphone charges.
An experiment-backed proof

Ibloo, a member of the renowned XDA developers forum, was able to prove (with detailed reports) that shorter cables charge faster than the longer ones. He performed an experiment using three (3) cables from the same manufacturer but of different lengths — 12, 36, and 72-inches respectively— and two different power adapter.

The cables were of the same wire/material and they and the same gauge/thickness. He used the three cables to charge the same device (a Samsung Galaxy Note 2) and proved the resistivity theory right; the shorter the cable, the faster the charge. Attached below are graphical representation of Ibloo’s findings.

The shorter cables (12 & 36-inches) supplied more power to the battery for both the Samsung & Asus adapters than the longer cable.

Output for each cable length


Now that you know that the length of a cable can impact the charging speed of your device, you should pay more attention to the type of cables you buy and also, cables you use to charge your device. When picking up a cable for your phone, ensure that it is thick and moderately sized length-wise. If you care about fast charging, shy away from using slim cables that are ridiculously long.
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