Galactus (fed) 120
Agamotto (in his own realm) 120
Silver Surfer 10
Dr. Strange 9 (but could be higher if bringing prep or various magical items to bear)
Once upon a time, Arishem would be even higher given that he effortlessly withstood the combined blast of three skyfathers, but the stock of Celestials have come down a lot since. Galactus and Agamotto stalemated in Agamotto's realm so I rated them the same. Dormammu, as boastful as they come, merely claimed to be the equal of Odin and Zeus, and that Odin and Dormammu were pitted in a chess match by Order and Chaos would seem to bear that out.
Always thought that Dormammu should be higher than that but the showings do not bare it out.
The only instance I can think of was a note in Dr. Strange. That the longer Dormammu was in the normal universe the stronger he would get until he would defeat even the Celestials. Or his showings of sort of canceling out Eternity in the one instance or defeating him with Umar. But both have asteriks with them.