It varies quite a bit by design, apparently the USSR’s initial design was only 15-20% fusion while US designs where closer to 50% which is still apparently the most efficient option in terms of warhead size.

However it’s possible to have higher fusion ratios at the expense of a larger device for the same yield. Most notably in the case of the Tsar Bomba’s which reduced the contribution of fission and too massively reduce the amount of fallout produced.