The interrupting curve drops to 154 kA at 415 V, 121 kA at 440 V, and 17 kA at 690 V, so size the breaker to the available fault current at your system voltage.
Ratings and thermal performance
Above that, it steps down: 19.2 A at 55 °C, 18.8 A at 60 °C, 18.4 A at 65 °C, and 18 A at 70 °C.
That 76.2 mm width — three modules on a standard 25 mm DIN-rail pitch — is what determines how many breakers fit in a row. The 70 mm depth matters when the enclosure backplate has limited clearance to the door or a rear bus.