Determining AM transmitter power output

How do I measure/calculate the power output of an AM transmitter?

 

Acknowledging my current situation, buying or building an RF power meter seems like a bit of an overkill. However, I may consider doing either or both in case I get myself a normal transmitter with the intent of using it regularly. I happen to own a certain type of low power transmitter which I don't use for obvious reasons but I'm still curious what is its power output anyways. The said transmitter would need to have an inductive coupling installed because otherwise putting anything conductive across the output would short the transmitter power suply, resulting in false reading at best or a damaged meter.
So for now, is there a way how to calculate the power without directly measuring it?

 

That would give me an estimated output power of 0,04314 W for the little transmitter. I also put together a more powerfull version of it, with which I briefly experimented back in 2019, and measured it's input power at 1,03056 W, giving the estimate of 0,51529 W at the output. I then disassembled it immediately, again for the same obvious reasons. I don't know if these figures are mediocre or laughable. Just to give me a sense of scale, could anyone, please, tell me what commercially available transmittes (or RC controllers or Wifi routers or whatever) operate at these power levels?