OnePlus 9 vs. Samsung Galaxy S21: Which Android phone wins?

Picking either the Samsung Galaxy S21 or the OnePlus 9 will result in you buying an excellent flagship Android phone. But if you want to find out which one's better for your needs, we need to examine the phones in more detail.

The Galaxy S21 effectively had the Android flagship market to itself for a little while in early 2021, but once the new OnePlus phone arrived, Samsung's claim to the Android throne was in question. The Korean company has a trio of well-received devices in the Galaxy S21 range. But as impressive as the S21 is, Chinese rival OnePlus has come out with a lower-cost alternative that matches or even bests Samsung's phone on some key features.

• OnePlus 9 vs. OnePlus 9 Pro: Biggest differences we've seen
• These are the best phones overall

This is only a two-way fight since for now, these phones stand by themselves at the top of the Android flagship world. Assuming you're not interested in an iPhone 13, the only other option you may want to consider is the Google Pixel 6. This, and the Google Pixel 6 Pro are both excellent phones in their own right.

One other thing to consider is the two new versions of these phones. The Galaxy S22 is expected to arrive in February, while the OnePlus 10 Pro, although announced already, is coming probably around March or April. If you want either company's latest and greatest, it may be worth waiting.

We think the Galaxy S21 might have met its match with the OnePlus 9. Although both deserve a position in our best Android phones guide, it's hard to figure out which one deserves the higher spot. Our breakdown of each phone's features below will help you decide which one suits your needs better.

OnePlus 9 vs. Samsung Galaxy S21 models

At its OnePlus 9 launch event on March 23, OnePlus took the wraps off two phones — the standard OnePlus 9 and a slightly larger OnePlus 9 Pro model. Rumors of a lower cost OnePlus 9R proved to be only half-right. The phone is in development, but it's only supposed to ship in India.

Samsung, in contrast, offers three different models in its S21 lineup. Besides the standard Galaxy S21, your choices include a larger Galaxy S21 Plus and a tricked-out Galaxy S21 Ultra. 

We'll leave the OnePlus 9 Pro vs. Galaxy S21 Plus comparisons for later. At this time let's largely focus on how the OnePlus 9 compares to the main Galaxy S21 model.

OnePlus 9 vs. Samsung Galaxy S21 specs

OnePlus 9 vs. Samsung Galaxy S21 price and availability

Samsung set a low price standard at the start of the year with the Galaxy S21.The flagship phone starts at $799 — a $200 discount from the debut price of last year's Galaxy S20. For that, you get 128GB of storage; an extra $50 boosts the storage to 256GB. (And you may need that added capacity, as there's no microSD card slot on the S21.)

But the OnePlus 9 is even cheaper, with a starting price of $729. For $70 less, you get a phone with 8GB of memory and 128GB of storage. You can boost the memory and storage to 12GB and 256GB, respectively, though that costs an extra $100 — not $50 like it does with the Galaxy S21.

OnePlus sells the unlocked handset from its website, and you can find it from other retailers like Amazon also. If you want it with a cell contract, then T-Mobile is the exclusive carrier for the OnePlus 9.

• More: OnePlus 9 and OnePlus 9 Pro price — what you'll pay

While the OnePlus 9 will be available from a single carrier (as well as multiple retailers in April), the Galaxy S21 is widely available. Each major U.S. carrier offers Samsung's phone.

OnePlus 9 vs. Samsung Galaxy S21 design

On the surface, the OnePlus 9 looks an awful lot like the Galaxy S21. Both phones look to have flat displays and like Samsung's handset, the OnePlus 9 features a square camera array in the upper left corner on the back of the phone. (This is a departure from the OnePlus 8, where the rear cameras descended vertically down the center of the phone.) Samsung introduced a new contour cut design with the S21 that better blends the camera array with the phone's frame, so we'll see how the OnePlus 9 handles making the camera array less prominent.

One of the ways Samsung kept costs down on the S21 was by using plastic materials for the phone's case instead of the glass backs found on the S21 Plus and Ultra models. OnePlus went a similar route with the 9, using a fiberglass-reinforced plastic frame — aluminum is reserved for the OnePlus 9.

You get two color options with the OnePlus 9 — Astral Black and Winter Mist. The latter is the more eye-catching of the two, with a gradient refraction effect. We do like the fact that Astral Black does a good job repelling fingerprints. The Galaxy S21 offers four colors, with violet and pink joining more traditional gray and white options.

OnePlus 9 vs. Samsung Galaxy S21: Display

The OnePlus 9 offers the bigger screen of these two phones, with its 6.5-inch panel larger than the 6.2-inch screen Samsung includes on the Galaxy S21. (Once you go bigger, the OnePlus and Samsung phones are on equal footing, with both the OnePlus 9 Pro and S21 Plus featuring 6.7-inch panels.)

Samsung gave adaptive displays to its Galaxy S21 lineup, with all three phones able to adjust their refresh rate depending on the task at hand. Activities like scrolling get a faster refresh rate, while the screen slows down to preserve battery life when your activities are more static. In the case of the S21, the screen's refresh rate ranges between 48 Hz all the way up to 120 Hz.

The OnePlus 9 can also offer a 120Hz refresh rate, which is an upgrade from the 90Hz rate offered by the OnePlus 8 last year. However, only the OnePlus 9 Pro gets an adaptive display; the 9's refresh rate is either 60Hz or 120Hz, and you're the one that sets it.

You can get a lot of color out of the OnePlus 9 display, which recreates 199.4% of the sRGB color spectrum when set in Vivid mode. That percentages that drops to 104.1% when you adjust the display to Natural, which is in line with the 109.2% that the Galaxy S21 shows off. Colors are a little bit more accurate on the OnePlus 9, with a Delta-E rating of 0.27 compared to 0.29 for the S21. (Numbers closer to zero are better.)

If you prefer bright screens, though, opt for the Galaxy S21. It hit 711 nits of brightness on a light meter, just beating the 696 nits we measured on the OnePlus 9.

OnePlus 9 vs. Samsung Galaxy S21 cameras

It should be hard for the new OnePlus phones to measure up to the Galaxy S21, which we think is one of the best camera phones you can buy. Even if you don't opt for the impressive 108MP main camera and dual telephoto lenses on the more expensive Galaxy S21 Ultra, the S21 won't disappoint with its camera hardware. You get three lenses — a 12MP main shooter, 12MP ultrawide angle lens and 64MP telephoto lens. It's that last bit of optics that truly impresses, as the S21 can offer a 3x optical zoom and a 30x digital zoom. A Zoom Lock feature helps keep those zoomed-in photos from getting too blurry and out-of-focus.

In fact, software skills abound on Samsung's phones, with the S21 supporting features like an improved Single Take that produces multiple versions of the same shot with one press of the shutter button. All S21 models include Directors Mode, which lets you capture video from multiple cameras at the same time, allowing you to toggle between angles and even the front and rear lenses.

And yet, the OnePlus 9 cameras impressed us in our tests. OnePlus has typically come up short in the camera department, so credit to the company's partnership with camera specialist Hasselblad. The two firms are working to improve the camera experience on OnePlus phones, starting with color accuracy. It's an effort that's paying early dividends with the OnePlus 9.

You get three cameras on the back of the OnePlus 9, though you're free to ignore the dedicated monochrome lens. The stars of the show are the 48MP main sensor and 50MP ultrawide camera, both of which took excellent pictures that held up well against top phones from Apple and Google. We look forward to conducting further tests for a OnePlus 9 vs. Samsung Galaxy S21 camera face-off.

OnePlus 9 vs. Samsung Galaxy S21 performance

Flagship phones from Samsung and OnePlus tend to offer the same mobile processor, and that's the case here. Both the OnePlus 9 and Galaxy S21 use Qualcomm's Snapdragon 888 system-on-chip, which helped Samsung turn in a very strong performance when we tested the S21 in January. (The iPhone 12 family, and its A14 Bionic processor, still tops our testing, though.)

And yet, the OnePlus 9 beats the Galaxy S21, which we attribute to the RAM OnePlus includes in its phone. On Geekbench 5, the OnePlus 9 turned in a multicore score of 3,618, beating the S21's 3,302 result. The OnePlus 9 also fared better in our graphics test featuring 3DMark's Wild Life Unlimited. Here, the OnePlus phone produced a 34.4 frames per second result, edging out the 33 FPS score of the Galaxy S21. It's close here, but we give the nod to the OnePlus 9.

OnePlus 9 vs. Samsung Galaxy S21 battery life and charging

The Galaxy S21 features a 4,000 mAh battery, but that doesn't translate enough juice to land on our best phone battery life list. The demands of a dynamically refreshing display and a 5G drain a lot of the power. In our test, in which we have phones surf the web over cellular until they run out of power, the S21 turned in a below-average time of 9 hours and 53 minutes. We got that result with the screen set to refresh at 60 Hz. With the dynamic refresh rate turned on, battery life fell by 3 hours. Among the S21 models, only the Galaxy S21 Ultra and its 5,000 mAh battery really impressed on our battery test.

This is one instance where the OnePlus 9 is a clearly superior phone. It's got a bigger battery, at 4,500 mAh, and it puts that power pack to good use. In our battery test, the OnePlus 9 held out for 10 hours and 51 minutes. That's just shy of the 11-hour mark, which would have made the OnePlus 9 one of the longest-lasting phones we've tested.

Even more impressive, that time came with the 120Hz refresh rate turned on. Scaling back to 60Hz, we ran the test again, and only saw a 2-minute improvement. So OnePlus has figured out how to combat the hit on battery life that comes with a faster screen refresh rate.

The OnePlus 9's battery dominance extends to charging, too. With OnePlus' WarpCharge 65T technology, you can refill a battery at lightning speed. After 30 minutes of charging with the included charger, our drained OnePlus 9 was back to 98%. The Galaxy S21, which supports 25W charging, was back to 55% in that time. And Galaxy owners have to go looking for a charger, as Samsung doesn't include one with the S21.

OnePlus 9 vs. Samsung Galaxy S21 outlook

The definitive OnePlus 9 vs. Samsung Galaxy S21 verdict will have to wait until we get to more thoroughly compare the cameras of the two phones. But in other aspects, the Galaxy S21 has a serious competitor in the form of the OnePlus 9.

The new OnePlus 9 turns in a faster performance, lasts longer on a charge, and recharges in the blink of an eye. While the OnePlus handset also features a fast-refreshing display, the Galaxy S21 outdoes it with a dynamically adjusting refresh rate. Then again, the OnePlus 9 also offers all those features at a lower price than Samsung charges for its phone.

Camera junkies may want to hold off on a purchase, but for the rest of us, the deck seems pretty stacked in the favor of the OnePlus 9.