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 device 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.