How to make splitter split at a specific ratio or amount?

[Entropy]

I want to split my main bus belts depending on the amount or ratio so i dont need to use lots of balancers and it will easy to manage over-production.

[Fel]

There is no easy way, splitters give half to each side, both lanes are treated as separate entries so the right lane will give half to both right lanes and same for the left lane.
You can also tell a splitter to send everything in one direction except if that direction can't accept more (output priority).
You usually can make a pretty solid system by combining those two.

It's not that it is completely impossible to make a system that sends a specific ratio in a direction without relying on many splitters but you end up needing a lot of circuit network logic, especially if you want to make sure that each lane can get the surplus in case the other lane gets stuck because not everything is getting consumed.

In the majority of cases sending half, a fourth or only the surplus in a direction is enough to have a factory that works well, if you really need a specific ratio like 3/5 to the right and 2/5 to the left for example, odds are you are going for something extremely complex that might be easier to solve in a different way that is much easier to handle.
For example, dedicated belts with the correct ratio of machines producing the item for each.

[Entropy]

Thanks for the detailed answer. I figured out that i am actually over-complicating things with that demand, thus i should choose simpler solutions if applicable. As you said, design change seems better

[impetus_maximus]

you could use a timer to adjust a splitter.

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play with the values to suit your needs.

[Sistermatic™]

I have only one thing to say.

Overproduction in Factorio is the ideal, not the exception. :)