20W or 30W: the difference in minutes
The short answer
For iPhone 16 and earlier, iPhone Air and iPhone 17e, a 20W USB-C charger is the right fit. A 30W charger saves only a few minutes on a full charge, even on Pro Max models that can draw about 25–30W. 12 For iPhone 17, 17 Pro and 17 Pro Max, Apple's fastest charge needs 40W or more. iPhone 18 Pro needs 60W with Adjustable Voltage Supply (AVS). 20W still charges these models, just more slowly. 34
In 30 seconds
- Your iPhone decides how much power it takes. A bigger charger cannot push more in, and it cannot "overload" the phone.
- The gain is front-loaded. Extra watts help most from empty to about 50%, and matter little near full.
- Match the charger to the phone: 20W up to iPhone 16 Pro Max, Air and 17e; 40W or more for iPhone 17 series speed; 60W AVS for iPhone 18 Pro.
How much faster is 30W, really? Model by model
All figures below come from independent tests. Each line names the iPhone, the adapters compared, the measure and the source. Tests differ in method, so compare within a row, not across rows.
| iPhone | 20W result | Larger-adapter result | Difference | Source |
|---|---|---|---|---|
| iPhone 15 Pro Max | 0–100% in 2 h 21 min | 30W: 2 h 11 min | about 10 min on a full charge | 9to5Mac, Oct 2023 1 |
| iPhone 15 Pro Max | average 18.65 W drawn | 35W: 24.85 W average | about 6 W more on average | ChargerLAB data via 9to5Mac, Sep 2024 5 |
| iPhone 16 Pro | 0–100% in 2 h 6 min | 30W: 2 h 2 min; 140W: 1 h 59 min | 4–7 min on a full charge | ChargerLAB, 25 °C chamber, Dec 2024 2 |
| iPhone 16 Pro Max | average 18.86 W | 35W: 30.55 W average | about 12 W more on average | ChargerLAB via 9to5Mac 5 |
| iPhone 17 | 50% in 27 min, 80% in 52 min, 100% in 1 h 50 min | 40W: 19 min, 44 min, about 1 h 42 min | 8 min to 50%; about 8 min to full | ChargerLAB data via Notebookcheck, 25 °C, Nov 2025 46 |
| iPhone 17 Pro / Pro Max | not tested on 20W | peak about 36–39 W on 40W+ adapters | Apple specifies 40W+ for 50% in about 20 min | MrMad (ChargerLAB data) 7; Apple 3 |
| iPhone 18 Pro / Pro Max | not tested on 20W | peak 52 W; 50% in about 15 min with a 60W AVS adapter | Apple specifies 60W, AVS, USB PD 3.2 | MacRumors, Sep 2026 8; Apple 3 |
- iPhone 17 · 20W
- iPhone 17 · 40W
Show the numbers
| Series | Battery (%) | Time (min) |
|---|---|---|
| iPhone 17 · 20W | 50 | 27 |
| iPhone 17 · 20W | 80 | 52 |
| iPhone 17 · 20W | 100 | 110 |
| iPhone 17 · 40W | 50 | 19 |
| iPhone 17 · 40W | 80 | 44 |
| iPhone 17 · 40W | 100 | 102 |
Show the numbers
| Adapter | Time to full (min) |
|---|---|
| Apple 5W | 436 |
| Apple 18W | 128 |
| Apple 20W | 126 |
| Apple 30W | 122 |
| Apple 140W | 119 |
Why the gap is small on a full charge
Your iPhone charges fastest when the battery is low, then slows itself down as the battery fills. Past roughly 80% it charges gently whatever the adapter, to protect the battery. 910 A bigger adapter only helps during the fast phase, and only if the phone can draw more than 20W. iPhone 16 Pro Max can draw about 30W 11, so a 30W adapter helps in the first half hour. After that, both adapters spend the same time topping up.
Why iPhone 17 and 18 Pro are different
From iPhone 17, Apple uses a newer USB Power Delivery mode called Adjustable Voltage Supply (AVS). It lets the phone request fine voltage steps at higher power, and it needs an adapter rated 40W or more (60W for iPhone 18 Pro). 123 A 20W adapter cannot offer AVS, because the mode applies only to adapters of 27W and above. 12 So on these models a 20W charger works, but it cannot reach Apple's advertised times.
When 20W is the right buy
- You have iPhone 16, 16 Plus, 16e, any iPhone 15, iPhone 14 or earlier, an iPhone Air or an iPhone 17e. Apple's own requirement is an 18W or higher adapter for iPhone 15 and later 3, and for Air and 17e Apple quotes 50% in about 30 minutes on 20W. 3
- You charge overnight or at a desk, where a few minutes do not matter.
- You want the smallest, simplest single-port charger.
When to step up
- iPhone 16 Pro Max or 15 Pro Max and you often top up in short bursts: 30W saves a few minutes in the first half hour.
- iPhone 17, 17 Pro or 17 Pro Max: 40W or more for Apple's 20-minute figure.
- iPhone 18 Pro or 18 Pro Max: 60W with AVS and USB PD 3.2.
- Faster MagSafe on iPhone 16, 17 or Air: Apple specifies a 30W or higher adapter for the newer MagSafe charger. 3
- Charging an iPad or MacBook from the same adapter: more wattage helps.
The ERONIX Charge range, matched by model
| Your iPhone | ERONIX adapter | Why |
|---|---|---|
| iPhone 15 and earlier | Fermi20 · 20W USB-C | Meets Apple's requirement for these models |
| iPhone 16, iPhone 16 Pro / Pro Max, iPhone Air, iPhone 17e, faster MagSafe | Fermi30 · 30W USB-C | iPhone 16 and later can charge faster above 20W |
| iPhone 17 series | Fermi45 · 45W dual USB-C with AVS | Clears the 40W Apple specifies for the iPhone 17's fastest charge |
| iPhone 18 Pro / Pro Max, iPhone Duo | Entropy67 · 67W dual USB-C with AVS | Clears the 60W AVS requirement |
Myths
"A higher-watt charger will damage my iPhone." No. USB Power Delivery lets the phone request only what it can safely take. A 100W adapter and a 20W adapter offer the same 5 V and 9 V levels to an iPhone that wants them. 13
"30W charges twice as fast as 20W." The wattage figure is a ceiling, not a speed. On iPhone 16 Pro the full-charge difference was 4 minutes. 2
"20W won't charge iPhone 17." It does, steadily: 50% in 27 minutes and full in 1 hour 50 minutes in independent testing. 4 It simply cannot reach Apple's 20-minute figure.
"Fast charging ruins the battery." Heat and long periods at full charge are the main stresses on a lithium-ion battery. 14 iPhone manages its charging speed and slows down past 80%. 910
Frequently asked questions
Is 20W enough for iPhone 16 Pro? Yes, for fast charging as Apple defines it (18W or higher for iPhone 15 and later). 3 A 30W adapter finished a full charge 4 minutes sooner in ChargerLAB's 25 °C test. 2
Is 20W enough for iPhone 17? It charges iPhone 17 to 50% in about 27 minutes in independent testing. 4 Apple's 20-minute figure needs a 40W or higher adapter. 3
Can I use a 30W or 65W charger on an older iPhone? Yes. The iPhone takes only what it needs.
Does 20W vs 30W matter for MagSafe? For iPhone 15 and earlier, a 20W adapter gives up to 15W MagSafe charging. For iPhone 16, 17 and Air, Apple specifies 30W or higher for the newer, faster MagSafe charging. 3
Does a bigger charger run cooler? Not necessarily. Temperature depends on the design and the load. A bigger charger delivering 20W is working less hard than a 20W charger at full output, but that does not make it better for the phone.
Comparative caveats
Apple adapter results are third-party measurements with dates and conditions. They describe Apple's adapters, not ERONIX's. We do not claim it is faster or slower than any Apple adapter.