USB Power Delivery Calculator
Calculate USB power delivery wattage, charging time, and compatibility.
Covers USB-A, USB-C, USB-PD, and Quick Charge standards with charging speed estimates.
USB Power Delivery (USB-PD) has revolutionized device charging by enabling far higher power transfer over a single USB cable. Understanding USB power standards helps you choose the right charger, estimate charging times, and avoid slow-charging frustrations.
USB Power Standards Comparison
| Standard | Max Power | Common Use |
|---|---|---|
| USB 1.0 / 2.0 (5V, 0.5A) | 2.5 W | Mouse, keyboard |
| USB 3.0 (5V, 0.9A) | 4.5 W | Slow phone charging |
| USB Battery Charging (BC 1.2) | 7.5 W | Older phone chargers |
| USB-A 5V 2.4A | 12 W | iPad / phone fast charger |
| Qualcomm Quick Charge 3.0 | 18 W | Android fast charging |
| USB Power Delivery (PD) 2.0 | up to 60 W | Laptops, tablets |
| USB Power Delivery (PD) 3.0 | up to 100 W | Laptops, MacBook |
| USB PD 3.1 | up to 240 W | Gaming laptops, monitors |
The Charging Time Formula
Approximate Charge Time (hours) = Battery Capacity (Wh) / Charger Power (W) × 1/Efficiency
Where efficiency accounts for heat losses (typically 80–90%).
If battery capacity is given in mAh at a nominal voltage V: Battery Wh = mAh × V / 1000
Example: A 4,000 mAh phone battery at 3.7V nominal: Battery Wh = 4,000 × 3.7 / 1000 = 14.8 Wh
With an 18W fast charger at 85% efficiency: Charge time = 14.8 / (18 × 0.85) = 14.8 / 15.3 ≈ 0.97 hours ≈ 58 minutes
Why Charging Slows Near Full
Most fast-charging protocols (USB-PD, Quick Charge) deliver maximum power until the battery reaches 70–80% charge, then taper off significantly. This “CC-CV” (constant current, constant voltage) charging cycle protects battery health. The last 20% of charging often takes as long as the first 80%.
Cable Matters
High-power USB-PD (above 60W) requires a USB-C cable rated for 5A. A standard 3A cable limits power to 60W even if the charger can deliver more. Always use the cable rated for your charger’s maximum power.
The charger is not the bottleneck, usually
The thing nobody mentions when selling you a 240W brick: USB Power Delivery is a negotiation, and the device sets the terms. Plug a phone into a 240W charger and it asks for the 25 or 45W it was designed to accept, gets exactly that, and charges no faster than it would on a 45W charger. The extra capability is real, but it is for the laptop you plug into the same charger later, not for the phone.
So the number that actually determines your charging time is whichever is smaller: the charger’s output, or the device’s input ceiling. Phone ceilings run roughly 20 to 45W for most models, with a handful of Android flagships going to 65 or 120W. Laptops range from 45W for a thin ultrabook to 140W or more for a workstation. If you know yours, put it in the optional field above, because otherwise this calculator will happily assume your phone can swallow 240W and tell you it charges in five minutes.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.