Alright, time to do some maths, which will contain a few assumptions. This is solely on Goku (with exception to 100% FP Frieza, his assumed power level when 'enhanced' and an estimate of Trunks' power level).

The following are the amplifications of Goku's power level in his base form:

Great Ape - 10x

SSJ - 50x

FPSSJ - 75x (probably wrong)

SSJ2 - 175x (as above)

SSJ3 - 400x (as above)

SSJ Great Ape - 500x

SSJ4 - 1250x

Theoretical SSJ5 - 3000x (just to see how big of a number after my calculations would be. I'm not saying he achieved this form, but by assuming he had access to it at the very end of GT)

Ok, now to list the power levels that we DO know:

Start of DB: 10

22nd Budokai (i think): 180

Fight with Raditz: 416

Fight with Nappa and Vegeta: 8,000 (32,000 with 4x Kaioken)

Fight with Ginyu Force: 90,000 (180,000 with 2x Kaioken)

Fight with Frieza: 3,000,000 (150,000,000 SSJ)

With the following calculations, I have based my assumptions on Goku telling Gohan (when he came back from otherworld (not sure if it were in the manga)) he thought Gohan would be twice as strong as when he fought cell, again assuming he trained for the full 7 years. Thus, 7 years of training = 2x previous power level at base. This is most likely wrong, but I to try to calculate the power levels after the Frieza Saga, however massive they are. I also assumed that Mecha-Frieza is more powerful than 100% Final Form, but less than or equal to SSJ Goku on Namek. So for argument's sake, I'll assume the extreme. Then, I assumed Trunks' base power level to be 6,500,000, which means 325,000,000 in SSJ. This could make sense given Vegeta's reaction to the possibility of Trunks being Goku (again, I am referring to the anime here, so I am unsure whether his reaction in the manga was the same or similar, or no reaction at all). Now to calculate:

Return to Earth

9,000,000 base (could make sense given recovery from his battle with Frieza)

450,000,000 SSJ

After 3 Years of training (1.4375x base from above)

12,937,500 base

646,875,000 SSJ

After 1 year in the ROSAT (1,145x base from above)

14,824,218.75 base

741,210,937.5 SSJ

1,111,816,406.25 FPSSJ

The above does not make sense, given he powered up in front of Korin.

After 7 years training

29,648,437.5 base

1,482,421,875 SSJ

5,188,476,562.5 SSJ2

11,859,375,000 SSJ3

Start of GT

11,859,375,000 base

592,968,750,000 SSJ

2,075,390,625,000 SSJ2

4,743,750,000,000 SSJ3

5,929,687,500,000 SSJ Great Ape

14,824,218,750,000 SSJ4

End of GT (~100 years training)

338,703,750,000 base

16,935,187,500,000 SSJ

59,273,156,250,000 SSJ2

135,481,500,000,000 SSJ3

423,379,687,500,000 SSJ4

1,016,111,250,000,000 SSJ5 (theoretical)

I predict the power levels to be far greater than what I've calculated, based on assumptions. However, comparing the 1 quadrillion power level to his 10 when he first appeared pretty much implies he has no limit in power.