Samsung Galaxy S21 vs Samsung Galaxy S25 Ultra
Our Verdict: The Galaxy S21 and the Galaxy S25 Ultra are four years apart, which is enough for a real difference. The S25 Ultra has the better camera on paper, 200MP versus 64MP, and the S25 Ultra has the bigger battery of the two, 5000mAh against 4000mAh, which should mean longer between charges in day-to-day use. The S25 Ultra has the stronger screen, bigger at 6.8" against 6.2" and sharper at 505 PPI, and the S25 Ultra goes up to 1TB of storage, where the S21 5G tops out at 256GB. If you're on the S21 5G, the S25 Ultra is a real step up, but only worth it if the changes above matter to you.
Buying outright, the S21 5G starts at £145 SIM-free.
10 reviews 4.4
12 reviews
Prices updated 27 July 2026
Samsung Galaxy S21
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Samsung Galaxy S25 Ultra
|
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|---|---|---|
| Expert Rating | 4.1 10 reviews |
4.4 12 reviews |
| Screen | 6.2" | 6.8" |
| Display | Dynamic AMOLED 2X | Dynamic LTPO AMOLED 2X |
| Resolution | 1080 x 2400 | 1440 x 3120 |
| Pixels Per Inch | 424 | 505 |
| Rear Camera | 64 Megapixels | 200 Megapixels |
| Front Camera | 10 Megapixels | 12 Megapixels |
| Chipset | Exynos 2100 | Qualcomm SM8750-AB Snapdragon 8 Elite (3 nm) |
| Battery | 4,000 mAh | 5,000 mAh |
| Storage | 128GB, 256GB | 256GB, 512GB, 1TB |
| OS | Android 11 | Android 15 |
| SIM Type | Nano SIM | nano-SIM and e-SIM |
| Connectivity | Up to 5G | Up to 5G |
| Wi-Fi | 802.11 a/b/g/n/ac/6 | 802.11 a/b/g/n/ac/6e/7 |
| Bluetooth | 5.0 with A2DP, LE | 5.3, A2DP, LE |
| Dimensions | 151.7 x 71.2 x 7.9 mm | 162.8 x 77.6 x 8.2 mm |
| Weight | 171 grams | 219 grams |
| Water Resistance | IP53 - dust and splash protection | IP68 - Dust and water resistant over 1.5 meter and 30 minutes |
| Contracts | - |
£33.79/mo
£29.00 upfront |
| SIM-free | £144.99 | £569.99 |
| Prices updated 27 July 2026 | ||
| Deals | Deals | |
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Frequently Asked Questions
Which has the better screen, the Samsung Galaxy S21 or Samsung Galaxy S25 Ultra?
The Samsung Galaxy S25 Ultra has the bigger screen at 6.8" compared to the Samsung Galaxy S21's 6.2", the Samsung Galaxy S25 Ultra has the sharper display at 505 pixels per inch versus 424, and the Samsung Galaxy S21 uses a Dynamic AMOLED 2X panel while the Samsung Galaxy S25 Ultra has a Dynamic LTPO AMOLED 2X.
Which has the better camera, the Samsung Galaxy S21 or Samsung Galaxy S25 Ultra?
The Samsung Galaxy S21 features a 64 Megapixels rear camera, while the Samsung Galaxy S25 Ultra has a 200 Megapixels rear camera. Both devices also have front-facing cameras for selfies and video calls.
Which is cheaper to buy SIM-free, the Samsung Galaxy S21 or Samsung Galaxy S25 Ultra?
The Samsung Galaxy S21 is cheaper SIM-free, starting from £144.99.
What storage options are available for the Samsung Galaxy S21 and Samsung Galaxy S25 Ultra?
The Samsung Galaxy S21 is available in 128GB, 256GB, while the Samsung Galaxy S25 Ultra comes in 256GB, 512GB, 1TB.
What processors do the Samsung Galaxy S21 and Samsung Galaxy S25 Ultra use?
The Samsung Galaxy S21 is powered by the Exynos 2100, while the Samsung Galaxy S25 Ultra uses the Qualcomm SM8750-AB Snapdragon 8 Elite (3 nm).
Which is easier to carry and hold, the Samsung Galaxy S21 or Samsung Galaxy S25 Ultra?
The Samsung Galaxy S21 is the more portable of the two: it's 48g lighter at 171 grams, it's also the more compact phone at 151.7 x 71.2 x 7.9 mm.
Which is more water resistant, the Samsung Galaxy S21 or Samsung Galaxy S25 Ultra?
The Samsung Galaxy S21 is rated IP53 - dust and splash protection, while the Samsung Galaxy S25 Ultra is rated IP68 - Dust and water resistant over 1.5 meter and 30 minutes.
What operating system do the Samsung Galaxy S21 and Samsung Galaxy S25 Ultra run?
The Samsung Galaxy S21 runs Android 11 and the Samsung Galaxy S25 Ultra runs Android 15. This is one of the biggest factors when choosing between the two, as each ecosystem has its own apps, services and features.