Depends. The output voltage will drop under load. For example a GOOD fully charged 10 amp rated 18650 will likely put out no more than 3.7 volts under a 20 amp load.
But under a 10 amp load it may put out 3.9 volts.
And under a 5 amp load it may put out 4 volts or more.
If you are talking mechs and doing cloud builds figure on ~3.7 volts if a fully charged GOOD battery.