The Galaxy A51 has a 6.5" Super AMOLED Infinity O display with an FHD+ 1080 x 2400 pixel resolution with a 20:9 aspect ratio and a ~405 ppi density with Corning Gorilla Glass 3. The phone itself measures 158.5 mm (6.24 in) x 73.6 mm (2.90 in) x 7.9 mm (0.31 in) and weighs 172 g (6.1 oz). The phone is powered by an Exynos 9611 (10 nm) octa-core (4x2.3 GHz Cortex-A73 & 4x1.7 GHz Cortex-A53) chip and a Mali-G72 MP3 GPU. It comes with either 4GB or 6GB RAM and either 64GB or 128GB internal storage, which can be expanded with a microSD card up to 512GB. It comes with a non-removable 4000mAh lithium polymer battery. It also has an in-display optical fingerprint sensor.
The Samsung Galaxy A51 has a four camera setup arranged in an "L" shape located in the corner with a rectangular protrusion similar to that of the iPhone 11 and the Pixel 4. The array consists of a 48 MP wide angle camera, a 12 MP ultrawide camera, a 5 MP macro camera, and a 5 MP depth sensor. It also has a single 32 MP front facing camera, which sits in a small punch hole on the front of the screen. Both the front and rear facing cameras can record video up to 4K in 30 fps, as well as 1080p in 30 and 120 fps. The rear cameras also have Super Steady.
The Galaxy A51 comes with Android 10 and One UI 2. (One UI 2.1 via software update) The phone has Samsung Knox for added system security.