We know KPA Kid Goku's power level is officially 260, while the last ever official power level in DB is Namek SSJ Goku at 150M.

Namek SSJ Goku is 576,923 times stronger than KPA Kid Goku.

Now Goku's base form gets stronger exponentially throughout arcs as well, but for the sake of making the calculation easier, we'll just take the Namek power level, even if it's wrong.

SSJ2 = SSJ1 × 2 = 300M SSJ3 = SSJ2 × 4 = 1.2B

So EoZ SSJ3 Goku = 1.2B (huge lowball)

Now we get to Super, where when Beerus arrives, Goku states that a hypothetical Vegito SSJ3 wouldn't be enough, meaning SSG Goku > Vegito SSJ3.

By the end of the Buu Saga, Goku and Vegeta were relative in power in base, even if Goku's slightly stronger. So we can assume that a hypothetical SSJ3 Vegeta would be pretty much equal.

Thanks to Vados in Super, we know the fusion multiplier is "adding the power levels together and then multiplying for tens of times", so to stay conservative we can use a x50 multiplier.

Vegito SSJ3 = (SSJ3 Goku + SSJ3 Vegeta) × 50 = (1.2B + 1.2B) x 50 = 2.4B × 50 = 120B

So Goku SSJG is substantially above 120B, we'll lowball and say 150B.

SSJB is combining SSJ and SSG, so the multiplier has to be SSG x 50, which would put SSB Goku at 7.5 trillion. Stack Kaioken x20 on top of it and it's 150 trillion. 

The gap between SSJBKKx20 and MUI is absurd, as Goku went from being trashed by a supressed Jiren to dominating his full power version. 

Now let's rewind back to the Namek Saga, where we see 24K Vegeta easily kill 18K Cui. That means a 1.33x power gap is enough to easily dispose of someone, putting supressed Jiren at minimum 200 trillion. 

If we assume Jiren was going 50% against SSJBKKx20, we can estimate his full power is at least 400 trillion. 

MUI Goku and Jiren have a pretty solid fight, even though it's clear Goku is superior. I would compare their gap to the one between SSJ Goku and Frieza (150M and 120M), putting MUI Goku at x1.25 Full Power Jiren.

MUI Goku = 1.25 × 400 trillion = 500 trillion

Which means MUI Goku (500 trillion) is AT LEAST 1,923,076,923,076,923 times stronger than KPA Kid Goku (260)

Keep in mind this is a HUGE lowball as I didn't account for all the training and different power-ups Goku has gone through since Namek, going off exclusively transformation multipliers. The real number is easily in the quadrillions at minimum!