My question is I have a 250 gallon Water heater do I calculate at 100% or 125%? This is branch circuit not feeder calculations. Thanks

That's a big tank.
Is this for a locker room with showers?

OK I see article 422.10 says 125% but where is the code reference to the breaker size one size higher? My water heater is listed at 87 A so 90 A is next standard breaker size.

You need to take 125% of the full load current; so it needs to be treated as a 108.75A load.
Make sure to also upsize the wire accordingly.

Thanks, ghost.
H20

Yeah exactly gym inside google bldg.
H20