That's for UIS which I lowballed MUI at because the actual multiplier for MUI is kind of too insane to just throw out there.
In short, VSBW has it accepted that God is At least 160,000x, Blue is at least 50x that (So >8,000,000x) and that fusions are accepted as stronger than their fusee's strongest forms combined in base form. So for example
Base Gogeta in Broly is scaled above X20 Blue Goku and SSBE Vegeta combined.
In the Moro Saga it is shown that Moro can counter Spirit Fission via speed blitzing. Yet Piccolo states Fusion is useless against Moro due to Spirit Fission being copied. Which Goku appears to agree with. That implies relativity between Moro-73 and Gogeta Blue (No Potaras, Piccolo saw Gogeta Blue, Gogeta has only gone up to Blue so far, Gogeta has no reason to hold back here). Enough for Moro-73 to land hits to defuse him.
Then we see UI Goku completely stomp Moro-73 with zero difficulty. Making it clear that UI is a greater trump card than the Fusion Dance.
That leaves two routes. Lowball (SSB x SSB via Base Gogeta > SSB Goku) or highball (SSBE x SSB via Base Gogeta > SSBE Vegeta/UIS Goku)
- SSB x SSB = 8,000,000 x 8,000,000 = 64 Trillion
- SSBE x SSB = 400,000,000 x 8,000,000 = 3.2 Quadrillion
So via that logic MUI's multiplier is well beyond 64 trillion times Base or 3.2 Quadrillion times Base. And this multiplier would apply to similar forms such as UE, Beast, Orange and (probably) Black.
Take that wank as you will.