It's often said Super Saiyan is a base form x50 upgrade, SSJ2 is double that, and SSJ3 is eight times as powerful as SSJ (or 400x base form).
So if SSJ put Goku on a 1,000,000 power level echelon, SSJ3 would be around 8,000,000, we'll round up to ten million.
From SS3 to SS God is a huge, huge increase in power. So it's safe to assume this goes from millions to trillions (remember: SSJ3 Goku literally couldn't do anything to Beerus, who simply flicked Goku's forehead to defeat him; whereas the SS God transformation allowed Goku to fight toe to toe with Beerus.)
And if SS God is in the trillions, SS Blue, which is another massive leap, is probably in the quadrillions, if not the quintillions. Let's be conservative and say 50 quadrillion. Goku can also go Kaio Ken x20 as SS Blue, which would be 50 quadrillion times 20 = one quintillion.
SSJ Blue KKX20 was useless against Jiren, whereas Ultra Instinct Omen immediately put Goku on par with Jiren, at least before Jiren powered up. So there's another massive leap. We can assume it goes from a quintillion to sextillion, or even septillion.
Then Goku and Jiren continued getting stronger even beyond that, with Goku attaining MUI and Jiren tapping into his hidden power, presumably both of them surpassing even the levels of the gods. So it's not out of the question, IMO, that there powers would be in excess of decillions. I voted for off the scale.
You're not even counting that he got stronger in his base form as time went on. Although, the jumps to ssg and ssb are a little hyperbolic IMO. I think trillions.
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