| Hardware and OS | Realme Narzo 21 | Oppo A3s |
| Operating system | Android v11 | Android 8.1 (Oreo); ColorOS 5.1 |
| Processor | MediaTek Helio G85 (12nm) | Octa-core 1.8 GHz Cortex-A53 |
| Chipset | | Qualcomm SDM450 Snapdragon 450 (14 nm) |
| RAM | 4 GB | |
| GPU | | Adreno 506 |
| Internal Storage | 64 GB | |
| Internal memory | | 16 GB, 2 GB RAM |
| External memory | | microSD, up to 256 GB (dedicated slot) |
| Display | Realme Narzo 21 | Oppo A3s |
| Type | IPS LCD | IPS LCD |
| Size | 6.5 inches | 6.2" inc |
| Resolution | 720 x 1600 Pixels | 720 x 1520 px |
| Touchscreen | Yes, Capacitive Touchscreen, Multi-touch | capacitive touchscreen |
| Aspect ratio | 20:9 | |
| Screen-to-Body Ratio | | 81.2% |
| Display area | | 95.9 cm2 |
| Display aspect ratio | | 19:9 (height:width) |
| Pixel Density | 270 ppi | 271 PPI |
| Colors | | 16M |
| Connectivity | Realme Narzo 21 | Oppo A3s |
| Network support | 4G , 3G, 2G | |
| NFC | Yes | |
| 2G Network | | GSM 850 / 900 / 1800 / 1900 - SIM 1 & SIM 2 |
| Dual SIM | Dual SIM, GSM GSM | |
| 3G Network | | HSDPA 850 / 900 / 2100 |
| SIM size | SIM1: Nano, SIM2: Nano | |
| USB connectivity | Mass storage device, USB charging | |
| 4G Network | | LTE |
| Wi-Fi | Yes, Wi-Fi 802.11, b/g/n | Wi-Fi 802.11 b/g/n, WiFi Direct, hotspot |
| Network | | GSM / HSPA / LTE |
| SIM card | | Dual SIM (Nano-SIM, dual stand-by) |
| Bluetooth | Yes, v5.0 | 4.2, A2DP, LE |
| Edge | | Yes |
| GPRS | | Yes |
| GPS | Yes, with A-GPS, Glonass | Yes, with A-GPS |
| Speed | | HSPA 42.2/5.76 Mbps, LTE-A (2CA) Cat6 300/50 Mbps |
| USB | | microUSB 2.0, USB On-The-Go |
| Camera | Realme Narzo 21 | Oppo A3s |
| Front camera resolution | 8 MP Primary Camera | |
| Camera features | Digital Zoom, Auto Flash, Face detection, Touch to focus | |
| Flash | Yes, LED Flash | |
| Autofocus | Yes | |
| Video recording | Yes | |
| Main camera | | 13 MP, Dual |
| Specs | | 13 MP, f/2.2, AF
-2 MP, f/2.4, depth sensor |
| Features | | LED flash, HDR, panorama |
| Video | | 1080p@30fps |
| Selfie camera | | 8 MP, Single |
| Multimedia | Realme Narzo 21 | Oppo A3s |
| Audio jack | 3.5 MM | |
| Loudspeaker | Yes | |
| 3.5 mm Jack | | Yes |
| Radio | | FM radio |
| Design | Realme Narzo 21 | Oppo A3s |
| Height | 164.5 mm | |
| Width | 75.9 mm | |
| Thickness | 9.8 mm | |
| Colours | Glory Silver, Victory Blue | |
| Colors | | Red, Dark Purple |
| Dimensions | | 156.2 x 75.6 x 8.2 mm |
| Weight | 208 grams | 168 g |
| Battery | Realme Narzo 21 | Oppo A3s |
| Capacity | 6000 mAh | |
| Type | Li-Polymer | |
| User replaceable | No | |
| Battery capacity | | 4230 mAh, Non-removable Li-Ion |
| Other | Realme Narzo 21 | Oppo A3s |
| Fingerprint sensor | Yes | |
| Fingerprint sensor position | Rear | |
| Other sensors | Accelerometer, Proximity, Compass | |
| Release date | | 2018, July |
| Sensors | | Accelerometer, proximity, compass |
