Just depends on your opponents boosts, castle walls/red dragons etc and depends on what type of units you send.

If the player you want to attack has a well rounded defense (meaning a good amount of each troop type) the ratio will be worse as an attacker on any unit you send.

There is no way to calculate what you will lose exactly as it all just depends on too many factors :p if you want to go big tho I may suggest a wave strategy.

Wave 1 Fireballs because if you are going to attack for sure, fireballs take you defense at random meaning good chance to take out castle walls/red dragons

Wave 2 of infantry/calvary bombs. This will give your low end troops a chance to take out wall defense/red dragons.

Wave 3 final wave of all your units you want to end up sending :) waves 1-2 will make sure this wave takes out more defense for less of a loss.

I should have asked it more specifically I guess. I know what happens when ppl send attacks at me they just all die cos I have a lot of defending troops, all at lvl 30 and good castle defenses. I was wondering about does it work the other way around if I have an overwhelming force fully upgraded, boosted to max from dragon arts and with good equipment?

I'm hesitant to send out large scale attacks at castles cos I fear losing a lot for taking down little (I know that castle ratios always look bad for the attacker and generally are like that cos of wall defenses) But I figured it has something to do with the overwhelming force in addition to everything else. I don't want to end up losing 10 million offense for no real results.

The wave attacking I implemented already, and it does alleviate damage to the last wave, fireballs come in handy for taking out defense, but I never send out attacks stronger than 1.5 mill. I just wondered if I went all out in that 3rd wave would I end up losing less troops or the same if I sent out a smaller force and would I kill more troops or the same amount. Not rly sure how to word it better... Let's just say I can kill the castle if I want to I just want to lose as little troops as possible in the process so does a bigger attacking force minimize my casualties or I lose the same amount in any event?

Ah I see what your asking. The answer is no, you will lose about same amount of offence sending a bunch of small ones rather than overwhelming force. Beacons, castles, and hamlets all will have same effect (generally) whether you send overwhelming force or small attacks. 

Fortress will switch the ratio for attackers with an overwhelming force but thats a huge one. Fortress's are crazy because sending small attacks do like no damage but send at least double what the defenders have and you get the ratio to be in favor of you.

Now that's a shame, I knew about the fort, I remember in the time when we started to climb past lv5 and before we racked it over 200 mill we always prayed all together when a top ranked player sent a test hit. Tough days, but the fort is safe once you got a lot of tings inside everyone just stays away. Beacons fall too fast in my opinion and naps is rly what holds them together.

I thought it might be the same if I do it for castles too, but in that case I will continue to do what I've been doing up until now, ratios for attackers are always bad no mater how much you upgrade your troops, but you have to attack when that turny shows up and our targets are always high lvl alliances.