Estimate how long a device takes to charge.
This estimate works from a charger's nameplate rating rather than a single wattage figure: USB-C power delivery adapters are labelled with voltage and current pairs, and multiplying them gives the negotiated output. Subtract conversion and cable losses to get what actually reaches the cell, then divide the energy still missing from the battery by that figure. The charge-rate output in percent per hour is the most portable number here — it lets you compare adapters and cables against the same device without recomputing anything.
Charge time from charger nameplate
Charger watts = V x A; delivered = watts x (1 - loss); minutes = capacity x (100 - start) / 100 / delivered x 60
Printed on the adapter itself, usually as a list such as 5V/3A, 9V/3A, 20V/3.25A. Use the highest pair both the charger and the device support, since they negotiate down to the lower of the two.
Yes. A cable not rated for the current will limit the negotiated profile or add resistive loss, and long thin cables are noticeably worse. Raising the loss figure to 18% or 20% is a fair way to model a marginal cable.
Because it assumes a constant rate throughout. Real charging tapers in the final fifth, so treat the result as accurate to about 80% state of charge and add time beyond that.