There is no single vent size that suits every container. In this walkthrough, Channing introduces the smaller BigAir 30 and larger BigAir 60 alongside the familiar 45, then installs a 45 to show what the wall actually needs to accommodate.
The size depends on the available wall
The 30 is for a smaller opening when cutting a larger hole is a concern. The 60 comes into its own when containers are parked close together and there are fewer exposed walls available for vents. The 45 sits between them as the familiar general-purpose choice. The video is clear that placement matters as much as the size printed on the box.
A useful installation lesson
For the 45 installation, the paper template is placed on the outside corrugations. Channing checks that the vent flange will have metal to fasten to before marking the cutout. Once the opening is cut, he seats the vent, drills the mounting holes, fastens it, and seals the edges. He also shows the screen mesh option for people who want a barrier to insects.
If you are planning two passive openings, he suggests putting one high and one low on opposite ends. That creates a path across the container. Check the exact template and mounting instructions for whichever size you choose; the video’s cutout demonstration is for the 45.
Watch the original full-length video or read the source post. This article is a practical summary of the spoken walkthrough; always use the instructions supplied with your exact product.