How to check your USB-C charger’s wattage on a Mac

The quick answer

Plug in the charger and run:

system_profiler SPPowerDataType | grep -A10 "AC Charger Information"

    AC Charger Information:

      Connected: Yes
      ID: 0x7002
      Wattage (W): 94
      Family: 0xe000400a
      Serial Number: C4H1...
      Name: 96W USB-C Power Adapter
      Manufacturer: Apple Inc.

Wattage (W) is what your Mac and the charger negotiated. That’s the ceiling for charging right now. The same section appears in System Information › Hardware › Power (hold Option and choose System Information from the Apple menu).

Volts, amps and what the charger offers

USB Power Delivery chargers advertise a menu of voltage and current pairs, and the Mac picks one. ioreg shows both the menu and the choice:

ioreg -rn AppleSmartBattery | grep -oE '"(AdapterDetails|UsbHvcMenu)" ?= ?.{0,400}'

In AdapterDetails, look for "Watts"=94, "AdapterVoltage"=20000 (millivolts, so 20 V) and "Current"=4690 (milliamps, 4.69 A). UsbHvcMenu lists every option the charger offered, for example:

5 V · 2.96 A   9 V · 2.97 A   15 V · 2.98 A   20 V · 4.69 A

If the top entry is 20 V at 3 A (60 W) on a charger sold as 100 W, the cable is probably the limit: it isn’t rated for 5 A.

Live input power

The negotiated wattage is a ceiling. To see how much is actually flowing in, read the power telemetry:

ioreg -rn AppleSmartBattery | grep -oE '"System(PowerIn|VoltageIn|CurrentIn)"=[0-9]+'

"SystemCurrentIn"=721
"SystemVoltageIn"=20472
"SystemPowerIn"=14766

SystemPowerIn is in milliwatts: 14.8 W going into the Mac at that moment. With a full battery and a light workload, that number is small even on a 140 W charger. Start a build and watch it climb.

Why your Mac charges slowly

1. Charger too small. A 30 W charger on a 16-inch MacBook Pro barely keeps up under load.
2. Cable limited to 60 W. Common with cables that came with phones or accessories.
3. Hub or dock in the middle. Pass-through charging docks keep some watts for themselves, often 10–15 W.
4. Battery near full. Charging tapers above about 80%, and Optimized Battery Charging may hold it there on purpose.
5. Heat. A hot battery charges more slowly to protect itself.

The 16-inch MacBook Pro needs MagSafe 3 and a 140 W adapter for its fastest charging; over USB-C it takes up to 100 W.

Quick reference: common chargers

Charger	Usually negotiates	Enough for
30 W	20 V at 1.5 A	MacBook Air at light use, slow charging
60–70 W	20 V at 3–3.5 A	MacBook Air at full speed, 14-inch Pro at light load
96–100 W	20 V at ~4.7–5 A	14-inch MacBook Pro, 16-inch at moderate load
140 W (USB-C PD 3.1)	28 V at 5 A over MagSafe 3	16-inch MacBook Pro fast charging

The negotiated figure is the ceiling. The Mac draws less whenever the battery is full or the workload is light, which is why live input power matters more than the label for spotting a weak charger.

USB speed of everything else

The same tool lists the USB tree, with link speed and power drawn:

# macOS 15 Sequoia and later
system_profiler SPUSBHostDataType

# macOS 14 Sonoma
system_profiler SPUSBDataType

        USB3.1 Hub:
          Link Speed: 5 Gb/s
            USB3.0 Card Reader:
              Link Speed: 5 Gb/s
              Power Allocated: 4.48 W (896 mA)

Thunderbolt and USB4 devices are under system_profiler SPThunderboltDataType. If a fast SSD looks slow, check here first: a 480 Mb/s link speed means it’s running at USB 2. When a drive refuses to unmount, see why you can’t eject a disk.

Seeing it live

Stat Space’s Devices tab reads the same IORegistry data with no Terminal: the charger’s name and negotiated watts, volts and amps (for example 94 W · 20 V · 4.7 A), live input watts, what each USB-C or MagSafe port is doing and how much power it sends out, and the USB tree as hubs and devices with a speed chip and bus power like “288 of 900 mA”. It only reads while the tab is open, and refreshes charger draw every 5 seconds there. It’s free.