Realme C21 smartphone has a 6.50-inch touchscreen display with a resolution of 720×1600 pixels. Realme C21 is powered by an octa-core MediaTek Helio G35 processor. It comes with 4GB of RAM. The Realme C21 runs Android 10 and is powered by a 5000mAh battery. As far as the cameras are concerned, the Realme C21 on the rear packs a 13-megapixel primary camera with an f/2.2 aperture; a 2-megapixel camera with an f/2.4 aperture, and a 2-megapixel camera with an f/2.4 aperture. It sports a 5-megapixel camera on the front for selfies with an f/2.2 aperture. The Realme C21 runs Realme UI is based on Android 10 and packs 64GB of inbuilt storage that can be expanded via microSD card (up to 256GB) with a dedicated slot. The Realme C21 is a dual-SIM (GSM and GSM) smartphone that accepts Nano-SIM and Nano-SIM cards. The Realme C21 measures 165.20 x 76.40 x 8.90mm (height x width x thickness) and weighs 190.00 grams. It was launched in Cross Black and Cross Blue colours. Connectivity options on the Realme C21 include Wi-Fi 802.11 b/g/n, GPS, Bluetooth v5.00, Micro-USB, 3G, and 4G. Sensors on the phone include accelerometer, ambient light sensor, compass/ magnetometer, proximity sensor, and fingerprint sensor.