01Length matters less than thickness

Cable length does affect charging speed, but only a little with a good cable. A 2 m USB-C cable with proper power wires fast-charges a phone at full speed. What really slows charging is a long cable with thin wires inside, and you can't see those through the jacket.

Electricity has to travel to your phone and back, so a 2 m cable is really 4 m of copper in the power loop. Copper has a small resistance per meter, and that resistance turns some power into heat and drops the voltage that arrives at your phone. Double the length, double the loss. Use thicker wire, and the loss shrinks.

Voltage lost = current × resistanceAt 3 amps, every 0.1 ohm of cable costs 0.3 volts before the power reaches your phone.

02The numbers: 1 m vs 2 m vs 3 m

Cable makers rarely print wire thickness, but the copper math is standard. Here's the voltage drop along the power wires alone at 3 amps, the most a normal USB-C cable carries. Thicker wire has a lower AWG number.

Now put that next to the voltage the charger sends. At 9V, the common USB PD fast-charging level, losing half a volt on a good 1 m cable is minor, and the phone simply draws what it needs. Losing nearly 4 volts on a thin 3 m cable is a different story: the phone sees the voltage sag and backs off to a slower rate to protect itself.

Old 5V USB-A charging suffers most, because there's less voltage to spare. That's one reason a long cable plugged into an old cube feels painfully slow. Our explainer on watts, volts and amps covers why higher voltage helps.

The loss also shows up as heat. At 3 amps, a typical 2 m cable turns roughly 3 watts into warmth spread along its length, which is why a long cable can feel faintly warm during fast charging. That's normal. A hot spot at one plug is not.

03Why USB-C fast charging copes with long cables

USB Power Delivery raises the voltage instead of pushing more current. Twice the voltage at the same wattage means half the current, and cable loss falls with the square of current. That's why a 2 m USB-C cable on a 20W or 30W PD charger behaves almost identically to a 1 m one.

PPS chargers go a step further: the phone fine-tunes the voltage in small steps while it charges, so it can compensate for some cable loss. Samsung's Super Fast Charging uses this, which is covered in what PPS charging is.

04File transfers are where length really bites

Data signals degrade over distance much faster than power does. USB-C cables have rough maximum lengths for each speed when they're passive (no booster chips inside):

USB 2 (480 Mbps)

Up to about 4 m

USB 5Gbps

Up to about 2 m

USB 10Gbps

Up to about 1 m

USB4 40Gbps

About 0.8 m

Most long charging cables are USB 2 for data, which is fine for syncing and CarPlay but slow for offloading 4K video. If you transfer big files from a Pro iPhone or to a portable SSD, keep a short, fast cable for that job. USB4 vs Thunderbolt cables explains the top end.

05Is your long cable slowing you down? A 10-minute test

1. Start around 20 to 30 percent

   Fast charging runs at its peak when the battery is low, so differences show up best here. Close apps and keep the screen off.

2. Charge 10 minutes on the short cable

   Use the same charger throughout. Note the percentage gained.

3. Drain back and repeat with the long cable

   Start at the same percentage and phone temperature. A warm phone charges slower regardless of cable.

4. Compare

   Within a percent or two is normal. A big gap means the long cable is too thin or worn. On Samsung, a "Fast charging" label that drops to plain "Charging" with one cable is a clear tell.

Still slow with a good cable? The cause is probably elsewhere: see why your phone is charging slowly. And for the jacket question, braided vs regular cables has you covered.