Assuming your old compact was 35t small ring, with 25t on the back, would be approx 38gi. Therefore you'll need something like 42/30 on a non-compact chainset.
In case you dont know: 27(nominal wheel size) x 42 / 30 = 38
@conker started
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Assuming your old compact was 35t small ring, with 25t on the back, would be approx 38gi. Therefore you'll need something like 42/30 on a non-compact chainset.
In case you dont know:
27(nominal wheel size) x 42 / 30 = 38