How hot does have to be to get sunstroke?

Depends.: Sunstroke occurs when you get dehydrated and run out of sweat, so that your body's thermostat can no longer keep your body cool. Your body relies on water evaporation to stay cool. It's possible to get sunstroke on any reasonably warm day if you don't drink enough water to stay hydrated. The risk increases the hotter it gets, however.

Doesn't matter: Sunstroke occurs when you get dehydrated and run out of sweat, so that your body's thermostat can no longer keep your body cool. Your body relies on water evaporation to stay cool. It's possible to get sunstroke on any reasonably warm day if you don't drink enough water to stay hydrated. The risk increases the hotter it gets, however.