That should work fine. Typical moisture content of raw sawdust is very high, but products that are sold are typically around 5 - 20%, but can vary batch to batch (or tree-to-tree) and is also dependent on the drying technique of the manufacturer. The moisture holding capacity of the wood is also something to consider, but it’s hard to determine tree species from sawdust (sometimes it can be done with wood chips).
Calculating the initial moisture, then ammending to reach your final moisture content is the safest way to get consistent hydration, but not everyone has the time to analyze every batch of sawdust. In large operations this is crucial, but most people will hydrate until when squeezed hard only a few drops of water come off the substrate. I’d both weigh to determine initial moisture content and squeeze as you’re hydrating to get a good sense of how this substrate hydrates. It may also take a while to absorb, so add the water, mix it in, give it 15 minutes to absorb, mix it again, then assess. Maybe add 75% of the total water volume you calculated to reach your 60% moisture content, to see what it feels like, then slowly add the remaining 25% while squeezing to monitor if it starts to feel too saturated.
You could also set up some experiments that have varying amounts of water added to reach theoretical moisture contents (50%, 60%, 70%) and compare yields.