It’s worth checking out arenafilm who have a detailed database of filmbacks and lens combinations for various cameras.
Also dpreview have a review of sensor sizes for DSLRs.
I’ll try and keep a useful summary here.
| Company | Model | Film Back | aspect | Pixels |
| Arri | Alexa | 26.136 x 14.702 mm / 1.0290 x 0.5788” (Monitoring/EVF) | 16:9 | 3168 x 1782 |
| Arri | Alexa | 23.760 x 13.365 mm / 0.9354 x 0.5262” (ProRes) | 16:9 | 1920 x 1080 |
| Arri | Alexa | 23.760 x 13.365 mm / 0.9354 x 0.5262” (RAW) | 16:9 | 2880 x 1620 |
| Red | Epic | 5120 x 2700 |