so is there a way to calculate what size cooler you need for the microprocessor? also I assume the design of the cooler will be important as well as the size to be aable to fit it in the case?
There should be a TDP rating somewhere on the box or in user manuals, developers have them listed too, Intel's ARK for example.
Some cooler makers tell you how many watts their coolers can dissipate, stock cooler will nearly always be enough for a user who never overclocks. If one decides to overclock, he should buy aftermarket cooler, something like a 212 Evo is pretty popular, cheap and effective.
The big air coolers are about as effective as cheaper AIO units. Some, like Noctua's NDH-15 I think it's called , £70 or so air cooler usually beats similarly priced AIOs (it's heavy too). Air coolers are more reliable too, the only part that can break are the fans, while AIOs and CLLs (custom liquid loops) have way more ways to make your wallet cry.
Generally, the bigger the heatsink, the more TDP cooler can dissipate. If you think air cooler might not be enough, an AIO might do you good without breaking the bank completely. Cost about £50-£150 depending on quality and size. The general recommendation is 120mm rad space for each 100W of heat recommended at least, as in 240mm of rad space for up to 200W. Probably the most frequent problem are pump failures and pump noise on AIOs.
Next Step is Custom Loop. It's like AIOs, but look better (IMO) and are more effective than AIO, however, with enough parts in the loop you can easily be out of £500 or more money. The 120mm for up to 100W remains.
To answer the size question.
Air coolers will have to fit in the case, it's THE limiting factor of what kind of cooler you can fit onto your CPU. RAM clearance is important too, some air coolers are so big they can bend taller RAM sticks. AIO has the block and pump in one (hence AIO - all in one) and it fits in any case that has space for at least one 120mm fan/rad that's not too far from the cpu. Custom loops don't need even that, they just need space for rads and pump somewhere in the case.
Cooling sub-section will have more in-depth answers
