If there's two things you can count on being in a piece of Dragon Ball media, it's 1) lots of screaming and 2) Goku getting stronger. The latter is massively important to both the franchise and the character, because it cements the overall theme of Dragon Ball and of Goku; that limits are meant to be broken, and that we can always be better—maybe not stronger as in Goku's case, but better in the broader definition of the word. Goku's character is about breaking through his limits, a theme that has been with him since the first Tournament Saga of Dragon Ball and the Turtle School training that led up to it. Suffice to say, Goku getting stronger is a big part of the series, especially when you realize that it has occurred about 20 times throughout the series, and that's just counting the main instances of Goku breaking his limits.
Throughout the franchise, Goku has experienced major power ups about 20 times, and we're not just talking about the times he's gotten a new transformation. No, we're talking about the times when Goku went through training, a tough battle, a series of injuries or some other struggle that left him stronger than when he started. Part of the reason Goku always gets stronger from a struggle has to do with his Saiyan heritage, which equates to whatever doesn't kill him, only makes him stronger. Of course, some of Goku's power is also from his hard work and obsession with getting stronger or a new technique he learns. So, we decided to ranking all the times Goku broke his limits in order of the power it gave him, which also happens to be in chronological order.
21 TURTLE SCHOOL TRAINING
Let's start with the first time that we saw Goku train on screen. At the beginning of Dragon Ball, we knew that Goku was trained by his adoptive grandfather, but we didn't truly see him get stronger until after he met Master Roshi. After instantly learning the Kamehameha attack, Goku became interested in learning more from Master Roshi, eventually becoming his pupil along with Krillin.
Goku and Krillin then learned the ways of the Turtle Master, learning less about martial arts and more about life as he gave them strength-training exercises involving the delivery of Milk and other seemingly menial tasks, all of which results in Goku becoming much stronger than he already was.
20 THE "SACRED WATER"
Though Goku would continue to get stronger through his fights in the World Martial Arts Tournament, his second major increase in power wouldn't come until the middle of the Red Ribbon Saga, when he climbed Korin tower and met the martial arts master at the top.
Korin told Goku that if he could get the Sacred Water from him and drink it, he'd become much stronger, but as it turns out the exercise gained from attempting to grab the water from the speedy cat was the actual "sacred water" power up. By climbing the tower, he became stronger, by anticipating Korin's movements, Goku's mind became sharper and in learning to keep up with Korin's speed, Goku's agility was strengthened.
19 3 YEARS OF TRAINING
After the events of the Red Ribbon Saga and the Fortuneteller Baba Saga, Goku was able to revive Upa's father before setting off to train on his own across the world. No one actually knew what Goku did or where he went in those three years, but he came back stronger than ever and clad in an animal-skin outfit.
All that we know about Goku's training is that he took Master Roshi's advice to wander the world -- literally, which is where he was between his first and second World Martial Arts Tournaments. Whatever he did while he travelled the world definitely made him stronger, since he was able to take on much more powerful opponents this time around.
18 ULTRA DIVINE WATER
Korin lied about the Sacred Water, but he did actually have a magic water that could increase a person's strength. However, there was a catch, all those who have attempted to drink the water perished from it. But, this was not the case with Goku, who drank it, passed out for a bit, then woke up with a massive power level increase.
Though the exact nature of the water is unknown, one theory is that it was simply a strong poison meant to make someone stronger by putting them on the verge of fatality only to have them recover stronger. Whatever the case, drinking the Ultra Divine Water was exactly what Goku needed to defeat King Piccolo.
17 TRAINING WITH KAMI
At the end of the King Piccolo Saga, Goku met Kami, the guardian of Earth, so that he could revive Shenron and, in turn, his friends. While he was there, Kami warned Goku that Piccolo's son would try to take over the world in due time, and that only he could defeat him.
However, Goku would have to train under Kami's tutelage in order to combat Piccolo Jr., which is exactly what he did for three years, once again showing up at the next World Martial Arts Tournament. After training with Kami, Goku had become even stronger, especially when he took off his weighted clothing.
16 KING KAI'S TRAINING
Kami wasn't the last god that Goku would train with, since after his perishing in the beginning of the Saiyan Saga, he went to Otherworld to train with King Kai. King Kai's training was similar to that of Master Roshi and Kami, who both used weights to strengthen Goku's physical capabilities.
The main difference, however, was that Goku was training under ten times Earth's gravity, which put his strength to the test, eventually increasing it, as he could easily move on King Kai's planet by the end of his training. Additionally, King Kai also taught Goku the Kaioken and how to form a Spirit Bomb, techniques that he was able to use to take on Vegeta.
15 100X GRAVITY
Goku wouldn't stop at ten times Earth's gravity, however, since his next power up would come after training under 100 times Earth's gravity, a ridiculous step up from Goku's previous training that showed how much tougher things were going to get from there.
This training was actually by accident, since the artificial gravity on the spaceship that Goku was taking to Namek has malfunctioned. However, once Goku managed to gain control of the ship, he decided to keep the gravity as it was, using it to train during his long trip. Eventually, he was able to move freely in this intense gravity, which showed just how strong he had gotten.
14 POST-HEALING CHAMBER
Despite his newfound strength, Goku still met his match on Namek, getting mortally wounded to the point of having to be put in a healing chamber. However, as we know with Saiyans, when they recover from a near-death experience, they become stronger than the thing that pushed them to the edge.
This was exactly the case, as Goku's next power up came when he emerged from the healing tank. Goku was so powerful when he emerged that Vegeta thought he was a Super Saiyan, though we would eventually learn this wasn't the case, since that transformation wouldn't come until later.
13 SUPER SAIYAN
Speaking of Super Saiyan, Goku's next power up, and his final power up of the Frieza saga, was when he first turned into a Super Saiyan. The transformation was triggered by the death of Krillin at the hands of Frieza, causing him to go ballistic and gain golden hair and a massive power up.
This transformation was exactly what Frieza had feared from the Saiyan race, and it was the very transformation that would defeat him. With a huge power multiplier, Goku was now on the same level as Frieza, which is how he was able to beat him in the end.
12 TRAINING ON YARDRAT
During his fight with Frieza, planet Namek began to fall apart, eventually exploding. Goku was able to escape this explosion by finding a nearby space pod, which took him to planet Yardrat, where he decided to stay and train before coming home to Earth.
While Goku was there, he learned how to use the Instant Transmission Technique, which itself might not be a power-up per se, but we're certain Goku also got stronger during his time training, since by the time he got to Earth, he was able to go Super Saiyan at will, rather than just when he was angry.
11 HYPERBOLIC TRAINING WITH GOHAN
Fast forward to the Cell Saga, and Goku decided that he and Gohan should train for a year in the Hyperbolic Time Chamber, which only equated to a day outside. During this training, Goku achieved a number of milestones that powered him up even more.
Not only was Goku able to master staying in his Super Saiyan form for longer, staying in the form from his emergence until the Cell Games, he also perfected the form itself. Additionally, he was able to push Super Saiyan past its limits and increase his strength in the form, a form he ultimately decided against using to prevent slowing himself down.
10 TRAINING IN THE AFTERLIFE
At the end of the Cell Saga, Goku decided to stay in Otherworld to avoid attracting more danger to Earth. During this time, he continued to train with King Kai, and the results showed, since this was one of Goku's strongest power ups in Dragon Ball Z, resulting in a brand new Super Saiyan form.
During his training with King Kai, Goku was able to achieve and master Super Saiyan 2, which had only previously been achieved by Gohan. Additionally, he achieved a new form, Super Saiyan, a form with a much larger multiplier than the previous two Super Saiyan transformations, but one that also came at the expense of massive energy drain.
9 FUSING WITH VEGETA
The final power up to come in Dragon Ball Z, aside from the power that Goku would later receive to form a spirit bomb (which we're not counting), came in the form of Goku's Potara fusion with Vegeta. The resulting fusion, Vegito, could be a considered a power up, since it combined both warriors' power and multiplied it by tens of times.
Though this was only temporary, its worth mentioning since it increased Goku's power, and it is more-or-less transformation. Regardless, with his and Vegeta's power combined, Goku was able to overpower Super Buu in every sense of the word as Vegito, even when he was turned into candy.
8 MORE KING KAI TRAINING
Goku's first power up in the new age of Dragon Ball came in both Battle of Gods and the Dragon Ball Super saga that adapted its story. As Bulma's birthday party began, Goku was still training on King Kai's planet, and though it isn't explicitly stated, we can assume that Goku was getting stronger during this time.
Of course, this training would mean nothing when Goku faced Beerus in their first encounter, as the God of Destruction completely dominated him. Not even Goku's Super Saiyan 3 form—which was shown in Dragon Ball Z to be so powerful that just the transformation caused unnatural weather—was enough to defeat Beerus, which is why he had to rely on...
7 SUPER SAIYAN GOD
It was a good thing that Beerus wanted to fight a Super Saiyan God, or else he probably wouldn't have let Goku transform into one. By using a special ceremony, Goku was able gain the power of a god, becoming much slimmer and younger-looking as his hair and eyes turned red.
This was a major power up, one of the few ones that Goku did not have to train for, but a major one nonetheless. However, instead of simply giving Goku more power, it gave him a different kind of power, godly ki, which is much stronger and more potent than regular ki, making for one of Goku's most interesting power ups.
6 TRAINING WITH WHIS
Goku wouldn't just stop at becoming a god though, now would he? After learning that Vegeta had been training with Whis, he wanted to do the same, traveling with the Angel back to Beerus' world to learn all that he could from a God of Destruction's teacher.
During his training with Whis, Goku not only got stronger in his base form, he also gained a new form, Super Saiyan Blue. This form is also known as Super Saiyan God Super Saiyan, which describes how it works; Goku became a god, and still has access to that power, so he taps into it in his base form, then goes Super Saiyan using it, resulting in a brand new power up for the character.
5 HYPERBOLIC TRAINING WITH VEGETA
The first saga in Dragon Ball Super that wasn't adapted from a movie was the Universe 6 Saga, which depicted Goku and other Earth warriors fighting in a tournament against warriors from an alternate universe. In order to prepare for this fight, Goku and Vegeta headed to the good ol' Hyperbolic Time Chamber to train as much as they could.
On top of gaining some impressive beards, Goku and Vegeta also gained a ton of power from their training, which was most likely due to the fact that they chose to spar each other instead of train separately. By fighting with opponent's on their level, Goku and Vegeta were able to push each other to new limits.
4 FIGHTING HIT
There have been times when Goku has gotten stronger in the middle of a fight, but none of them are as flashy as his fight with Hit during the Universe 6 Saga. The assassin warrior has the power to jump ahead in time in, which gave him the upper hand during the fight.
However, Goku managed to push himself to combat this special ability, breaking his limits and coming up with a new technique of sorts to make himself stronger. By combining an old power up, the Kaioken, with a new power up, Super Saiyan Blue, Goku once again got stronger than he had once been, even if he lost the match in the end.
3 SIGNS OF ULTRA INSTINCT
Fast forward to the Tournament of Power in the Universal Survival Saga, and we have one of Goku's most interesting power ups, if it can even be called that. The reason we say this is that Goku's first signs of mastering Ultra Instinct were not the complete form, and because the form itself isn't really a power-related technique.
Instead, Ultra Instinct has more to do with the body becoming more efficient at fighting, with power playing a less important role. Even with just the early signs of Ultra Instinct, Goku was still able to best Kelfla in the Tournament of Power, which is super impressive given that they were a Potara fusion.
2 MASTERING ULTRA INSTINCT
The signs of Ultra Instinct were nothing compared to the completed form, which gave Goku silver-white hair and wrapped him in a crazy-cool-looking aura. With this power up, Goku had essentially become a god at fighting, since Ultra Instinct is a technique that even gods have trouble using.
But again, power doesn't really play a factor in Ultra Instinct, since the increased strength that Goku gets from the form comes from his body relying only on instinct and reflex, essentially deleting the delay between stimuli and response, making for a cool limit-breaking moment that marked Goku's last power up in of Dragon Ball Super.