You need a suitable charger to charge a phone quickly and reliably. The best smartphone chargers have built-in safety mechanisms and plenty of power, guaranteeing they’ll charge any modern Android phone. How can you tell if your charger charges your device as fast as possible? Finding out your phone’s maximum supported charge rate isn’t difficult. It’s trickier to tell how many watts are going into your phone’s battery. This guide shows you how to get the numbers.
What are watts, and how do they affect charging speed?
Making sense of the numbers
Watts indicate how much energy is generated, consumed, or transferred over time. The greater the number, the more energy is flowing. In the case of charging a battery, more watts mean faster charging. To calculate the watts flowing between two points in a circuit, multiply the voltage by the current (Watts = Volts X Amps).
The maximum charging rate of a phone is typically mentioned on its specs page or verified by independent lab reviews. Therefore, it should be easy to find out what your phone is capable of. In rare cases, a manufacturer may recommend a charger with a rating higher than what the phone supports. For example, Google launched the Pixel 7 Pro recommending a 30W charger, even though the phone tops out at 23W. Samsung, in contrast, recommends a 25W/45W for its Galaxy S24/S24 Ultra, matching their maximum charging rate.
How to measure charging power with an app
Using an app is a cost-efficient and speedy method for gauging charging performance. For quick results, we recommend the free Ampere app for Android. It measures the current going into your battery using an API that gathers the same battery and power data the operating system collects.
- Install the Ampere app from the Google Play Store and open it. After a quick UI tour, the app displays the current in milliamperes (mA) flowing in or out of the battery.
- Connect your device to the charger you typically use. A positive number shows the current at which the battery is charging.
- Multiply the current by the voltage displayed on the same screen. That’s how much power, in milliwatts (mW), is going into your phone’s battery. Divide the milliwatt number by 1,000 to convert it to watts (W). Using the data from the right image below, we can conclude the device is charging at 2.97 watts (770mA x 3,858V / 1000 = 2.97W).
There are several important things to note. First, phones charge faster at lower battery levels. Your battery should be very low, under 20% in some cases, to reach the highest power rates possible. As the battery fills, the phone draws less power to prevent overcharging or damaging the battery.
Second, voltage and current numbers may go up and down. That is normal. To get accurate measurements, do your calculations with voltage and current numbers taken at the same time.
Third, with Ampere, you won’t get the exact numbers you expected. The advertised charging rate for a phone is the maximum power it can draw from the charger. However, Ampere only measures the power going into the battery, which is less. The difference is consumed by the phone being on and lost to inefficiencies in its charging circuit. In a test I performed for this article, I got 18W coming out of my charger, but only 15W measured by Ampere. Still, your numbers should be close (within 75% or above). If they aren’t, there’s a troubleshooting guide below.
How to measure charging power using a USB power meter
A dedicated meter for better accuracy
Your primary alternative to using an app on your smartphone is to purchase a USB power meter. It’s more accurate than using Ampere and one of the best ways to tell if your charger works as well as it should. Here’s what to do:
- Purchase a USB power meter. Affordable versions are available for testing consumer devices like phones. The USB-C meter from Plugable is one of the best affordable options.
- Plug the meter into your device, and plug your charging cable into the meter. The gadget acts as an intermediary between the charging cable and the device.
- The meter shows a running measurement of voltage (V), current (A), and watts (W), so you don’t need to do the math we did using the Ampere app.
A physical device lets you switch between cables and chargers to see if any make an immediate difference. This is especially important because a cheap or damaged cable could be why a phone doesn’t charge as fast as it should.
Physical devices have limitations. The Plugable model mentioned does not support extended USB-PD power ranges of 28V or above, only supporting a 4-22V, 50mA-6.5A operating range.
Can changing the charger or cable make an Android phone charge faster?
Yes, using a lesser cable or charger can slow charging speeds, and upgrading can improve them. With the methods above, you can confirm if your phone is charging as fast as possible. If the power numbers are close to what the manufacturer advertises, your charging setup is performing properly. If they aren’t, consider the following:
- Try a different USB cable. Cheaper and lower-quality cables may not carry as much current as the one that came with your phone. Some phones, such as OnePlus models, may achieve top speeds with their proprietary cables only. Check out our picks for the best USB cables if you need a spare.
- Check if your charger can supply the power your phone supports. For example, if you want to charge a phone at 25 watts, the charger should be rated for 25 watts or more. The output power numbers should be listed on the charging brick, though you may need to multiply volts by amps to get its maximum wattage.
- Ensure the charger and phone support a common fast-charging protocol, such as USB Power Delivery, Qualcomm Quick Charge, or Adaptive Fast Charging. GaN technology is not a protocol and does not directly affect charging speeds.
- Try a different charging port. Some chargers have multiple USB outputs but support fast charging or a specific protocol on only one or some of them.
You’re ready to test your USB gadgets
Now you know how to see how fast your phone is charging and how to make sense of the numbers. Sometimes, upgrading the charger or cable may not change much. Slow charging could be the symptom of a failing battery. You can check the battery health of your smartphone to get a better idea of the shape it’s in. When shopping for accessories, buy from reputable companies that stand behind their advertised charging speeds.