New crankset, different top size, how many extra chain link pairs?

[SatNavSaysStraightOn]

Quick question from those understanding chain inch gears and the likes...
I have just changed from a 30/39/50 chainset on an 11-28 (8 speed cassette) to a 30/42/52 chainset with the same cassette. How many extra chain link pairs are going to be needed?

I'm guessing (and it is a guess) at 1 extra pair? But can someone confirm this for me please as my bike is still in bits and awaiting assembly.

thanks in advance
SNSSO

 

[Rohloff_Brompton_Rider]

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

 

[SatNavSaysStraightOn]

thanks - first comes out at 53 pairs, and new one comes out at 54... I was on 52... now on 53. 54 was clearly too many for my rear derailuer to handle.
Will see how we go - suspect my front dereailuer issues are just me and indexing and my inability at it...

 

[andrew_s]

For 2 extra teeth, you need half an extra pair of chain links.
Only one of the extra teeth is located on that part of the chainring that is in contact with the chain. Everything else is the same as before.