Does the length of the cable affect the charging time?


From smartphones to laptops, we charge multiple devices every day, and many of them use a USB cable to transfer power. But if we use a longer cable, will it take more time to charge the device? In the following article, we will examine this issue.

The length of a USB cable can affect how much power it transfers from one end to the other, but there are several other factors as well. Therefore, it is not easy to say that we will get slower charging speed with a long USB cable or that faster charging is always associated with a shorter cable. Before we talk about these issues, it seems necessary to understand the importance of cable length.


When the electric current flows through the wire, it is not completely free but encounters the resistance of the wire. This resistance will result in energy loss and ultimately voltage reduction. However, the resistance between the two points of the beginning and the end of the cable depends on several factors, including the length of the wire, its cross-section, temperature and construction material.

The longer the length of a wire, the more resistance the electric current will face; Therefore, a one-meter cable will have less resistance than a two-meter cable. Likewise, the resistance of a wire increases as the temperature rises; So if you charge a device when the ambient temperature is high, the resistance will be higher than when the temperature is lower.

However, resistance is inversely proportional to cross-sectional area. This means that if a wire is thicker, the current will encounter less resistance, but a thinner wire will have more resistance. In the United States, wire thickness is usually measured by gauge. It should be explained that a lower gauge number indicates a thicker wire and a higher number means a thinner wire. Therefore, lower gauge wires have less resistance and higher gauge wires have more resistance.

Long charger cable

Finally, electrical resistance depends on the material the wire is made of. Silver has the lowest resistance, followed by copper, gold and aluminum. USB cables and other cables are usually made of copper, as this metal is cheaper than silver. Copper alloys are also used to increase the physical strength of cables.

Overall, the length of the USB cable matters when it comes to charging speed. But is the voltage drop significant enough and do the cable manufacturers take this voltage drop into account?

Does using a longer cable cause slower charging?

Currently, it is known that a voltage drop may occur if a longer USB cable is used. But as mentioned, several factors can affect the amount of voltage drop, and the most important factor is the gauge of the wire. Temperature and construction material are not that important, as most USB cables usually have copper wire and the temperature of your environment won’t change with a short or long cable.

Since voltage drop is an undesirable factor, USB cable manufacturers usually take it into account and use lower gauge wires to reduce electrical resistance in long cables. If a manufacturer hasn’t done this, you may see a significant voltage drop on long cables, resulting in slower charging. Unknown and unreliable brands sometimes try to save money by using higher gauge wire in long cables.

The effect of USB cable length on charging

If the cable is certified USB-IF And if it is from a reliable brand, you will not face this problem. USB-IF or USB Implementers Forum is a non-profit organization that recommends minimum DCR (DC resistance) requirements while protecting USB standards. According to the specifications USB-IFthere should be no more than 500mV (0.5V) end-to-end voltage drop at the maximum rated current of the cable.

For example, to understand what a drop of 0.5 volts means for the phone’s charging speed, if you use a charger with a current of 3 amps and a voltage of 5 volts, your phone should ideally charge 15 watts, but due to the drop in voltage, 5 volts to 4.5 volts. will be converted and the charging speed of your phone will be only 13.5 watts. The maximum voltage drop for USB-IF certified cables is around 0.5V, which you will only see on long cables of two or three meters or longer.

If you are going to buy a long USB cable, look for a reputable brand with USB-IF certification so you don’t experience slow charging.

Apart from cable manufacturers, fast charging standards such as Qualcomm also pay attention to voltage drop in long and thin cables. As a result, these standards try to minimize charging problems and limitations by using high voltage.

Should we pay attention to the length of the USB cable?

Although technically the length of the USB cable can affect its charging speed, as a consumer, you don’t have to worry about it. Most people will probably never buy a USB cable longer than a meter or two, and the voltage drop is negligible for those sizes. If you want a longer USB cable, USB-IF certification and reputable brands can help. Always get charging cables and all accessories from reputable brands.

iPhone being charged via USB cable

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Adib Zahedi is the CEO and Founder of He has nearly a decade of experience in IT, including two years spent working on a Youtube Chennal. He is also an author and writes articles for Has articles include tutorials and covers everything from Windows PCs to smartphone's software.

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