The battery capacity of a cell phone, measured in milliamp-hours (mAh), is one of the most important considerations when buying a smartphone, but a less studied but almost as important factor is the charging speed of the phone.

Of course, this depends in part on the size of the battery. In general, a 6,000 mAh battery takes longer to charge than a 3,000 mAh battery. However, this is only part of the formula.

The charging time of a phone is also affected by the maximum support charging speed of the phone and the power of the charger you have. In some cases, you may be able to upgrade the phone's charging speed by purchasing a charger that is rated higher than the charger in the box (if included).

Below we have rounded up all the phones from our list of best phones and best Android smartphones to see how they compare to each other in terms of charging speed.

Using Apple's $19 20W fast charger, the iPhone 12 went from zero to 57% in a 30-minute charge test. The company has stopped shipping power adapters with the handset, so you will have to procure your own.

The iPhone 12 Pro was able to charge 50% in 30 minutes, and 55% when using a 20W Apple charger. The battery is on the small side at 2,815 mAh.

The iPhone 12 mini is even better, which is perhaps not surprising given that the battery is 588 mAh smaller. Still, it was able to reach 60% in 30 minutes.

The iPhone 12 Pro Max has the largest battery in Apple's lineup at 3,867mAh. Apple's 20W charger got this large screen phone to 47% in 30 minutes.

Some good news: the iPhone SE included a dedicated power adapter. The bad news. Our review documented that it took 30 minutes to reach 29%.

However, this could reach a very similar speed to the iPhone 12, as the iPhone 12 supports a maximum charging speed of 18W.

Asus' gaming smartphone is one of the fastest charging smartphones; the 6,000mAh battery comes with a 65W charger, and the Asus ROG Phone 5 can charge from 0% to 70% in 30 minutes. after 15 minutes it reached 44%.

The Google Pixel 4a comes with an 18W charger, which allows for just 50% battery after 30 minutes of charging. However, keep in mind that the capacity is low at 3,140 mAh.

The enhanced Pixel 4a 5G is slightly worse, but not enough to make us reconsider upgrading, especially considering its high 745 mAh capacity In 30 minutes, the included 18W charger took the phone from zero to 46%.

The MotoG Power's legendarily long stamina may guarantee it a spot on the list of longest cell phone battery life, but it takes quite a while to charge. In our tests, the battery was down to just 22% thanks to a slow 10W charger.

The WarpCharge 65T charger that comes with the OnePlus 9 promises a full charge in just 29 minutes; in our 30-minute test, the OnePlus 9 achieved 98% capacity.

The OnePlus 9 Pro also comes with the Warp Charge 65T charger, which achieved 99% battery capacity after just 30 minutes of charging at an outlet. This is the fastest charging phone we have tested. The OnePlus 9 Pro may lose its spot on this list, as recent rumors indicate that the OnePlus 10 Pro will have 125W charging, which is nearly double the 65W charging of current OnePlus phones.

As a slightly disappointing downgrade from the Note 10 Plus, which can charge at 45W, Samsung's Galaxy Note 20 Ultra only supports 25W speeds; in 30 minutes, the Galaxy Note 20 Ultra achieved a rather respectable 56%.

The Samsung Galaxy S20 FE offers what made the original S20 special at a greatly reduced price. However, cost savings have to be found somewhere. The Galaxy S20 FE got 35% in 30 minutes, but if you want more speed, you'll need to spend $29 for a 25W power adapter.

Like Apple, Samsung has decided to discontinue the power adapter with the S21 series, so speed will depend on the available plug. Nevertheless, tests with a 25W charger on a Samsung Galaxy S21 showed that it could reach 55% in 30 minutes.

Not only does the Samsung Galaxy S21 Ultra not come with a power adapter, but Samsung has reduced the optional 45W charging that was on the S20 Ultra to 25W here. Still, the phone goes from zero to 54% in 30 minutes, which is not slow.

Samsung's foldable beast, which actually has two batteries split in the afternoon on either side of the foldable screen, doesn't seem to affect the 25W charging speed much: in 30 minutes, the Samsung Galaxy Z Fold 2's battery reached 46%.