How do people convert cycling to running equivilant? Do most of you count it as 2:1 eg. 1 hour's cycling is worth 30 mins running?

This is what I've always done (although 1:1 for turbo training because it's continuous) but I've heard views ranging from 3:1 to 3:2. I try and keep pedalling on the downhills which maybe makes my bike rides 'worth' more...?