Frieza's second form is supposed to have a power level of over 1 million (often given as 1,060,000) In his final 100% form, Akira Toriyami states its 120,000,000. Yet in the English dub of Resurrection of F, Frieza while in his first form remarks to Sorbet, that with 4 months training, he could increase his power level to 1.3 million. Is Frieza really bad at math, or does he not know his own powerlevel, because he becomes a LOT stronger than 1.3 million. By the end of F, he's rumored to be in the septillions.
Freeza had never trained a day in his life, so he had NO idea how large of a gain he could actually achieve by training. 1.3m was just his laughably inexperienced guess.
That considered, his initial "estimation" ended up being grossly inaccurate in the end. After all, a PL of 1.3m would barely even register as a blip on Piccolo/Gohan's radar at this point... Yet Toriyama certainly went out of his way to show us that 1st form Freeza already VASTLY surpassed them, and moreover, was in the upper-echelon of ki they'd ever sensed(they were literally awestruck at his power.) That's why most agree 1st form Freeza(post-training)~Super Boo, at the very least.
You'll have to excuse Freeza's naivete. He literally had NO training experience whatsoever, thus had NO clue how powerful he could actually become.
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Um... It was 1.3 BILLION. Not million. And that was first form Frieza. He knew his own power level apparently quite well.
And his golden form is not anywhere near the septillions. A guess from a voice actor suggested it to be 100 quintillion. Two "illions", below septillion.
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"Why is everybody so ****ing stupid?"- Kim Jong Il, Team America.
Yeah, numerical power levels are ridiculous to try and approximate in current continuity(that's why Toriyama stopped using them.) They were very helpful up to the Freeza saga, though.