how long should you rest between sets when your goal is to add size(muscle)
like i said in the title,for muscle building. not necessarily optimal for strength,since if your main goal is strength then you will need to add more time to fully recover
so lets talk about how long is optimal for fully recover from set to set
so according to a recent study by Brad Schoenfeld that really tested longer rest periods(3-min) vs shorter (1-min) rest periods
conclusion: the longer 3 minutes rest periods. promote greater increases in muscle strength and hypertrophy.
this research only tested 3 min vs 1 min.
link to the research:https://www.ncbi.nlm.nih.gov/pubmed/26605807
other research suggests that two minutes may be enough to fully recover between sets,
i would recommend you resting in your big compound exercise like the: dead lift ,squats,bench press ,overhead press ,bent over row,pull ups to rest 2-3 minutes and even longer as long as you can still make progress (adding weight).
and for your accessory lifts,incline bench press,dips,leg press,lunges,Romanian dead lifts,pull down,rest in the 45-90 seconds, again this is in theory some days you will feel full of energy and good pump so rest shorter as little as 30-45 seconds and some days you will feel tired and the weight will just feel so good dam heavy.on these days rest 90-120 seconds. don't compromise your strength.
i like an itra(during)workout drink Gatorade( sport-drink)+ protein shake,so i can keep my energy levels high through my workouts.but that is used only if my pre workout wasn't to close to my workout.,and only for my longer workouts.