Volume pricing for apps with multiple instances/regions

I suspect this is pretty simple, but I want to make sure I understand it before receiving a surprising bill. (I’m ignoring the free 3 GB free allowance, so that this will apply at scale.)

Volumes are billed at 15¢/GB, and are locked to a region and app. So if I create a 1 GB volume for an app in IAD, I’ll only get charged 15¢/month.

I assume that multiple instances of the same app in the IAD region will all use the same volume, correct? So with 3 app instances in IAD and a 1 GB Volume, I’ll still only get charged 15¢ for the volume allocation.

However, if I want to expand the app to LHR, that will require me to create a separate volume for that region, meaning I’ll now be charged 30¢ for my two volumes, regardless of the number of instances in each region. Is that right?

So basically, the cost of block storage for an app is 15¢ per gigabyte per region, regardless of the number of app instances?

It is per instance. Instances don’t share a volume. See:

There can be multiple volumes of the same volume name in a region. Each volume has a unique ID to distinguish itself from others to allow for this. This allows multiple instances of an app to run in one region. Creating three volumes named myapp_data would let up to three instances of the app start up and run.

Volumes · Fly Docs

Ah, ok. Cool. That makes sense, just wasn’t entirely obvious from the documentation.