Converting to UK grades

My university doesn't have grade inflation and it has a rather strict guideline on how grades should be awarded. On average, around 45-50% of students will have a 2:1 or above, and only 10-15% get a first. It's significantly lower than in the UK.
We use a GPA system with the perfect score being a 4.3, and set our honours according to this marks. We actually have two GPAs, one for just major required modules and another for all modules.

1st - 3.6/3.4
2:1 - 2.85/2.7
2:2 - 2.15/2.0
3rd - 1.7/1.7

So I can say that a 1.7 is roughly a 40, 2.00 is a 48.5, 2.15 is a 50, 2.7 is a 58.5, 2.85 is a 60, 3.4 is a 68.5 and 3.6 is a 70. My last semester was a 3.12, so it's roughly in the high 63 to 64 range of the UK scale? How do you suggest me to convert it should I apply for postgraduate studies in the UK?