On page 249 of the DMG, under Adjudicating Areas of Effect, it has this table with conversions for estimating how many targets are hit with an area of effect spell when using a battle grid. I’ve found that in both of my current campaigns, bringing out the battle grid usually slows things down significantly, and doesn’t always add to the interest of the combat. Sometimes it’s just a fight and there aren’t a lot of interesting tactical options available, but people still spend more time counting squares and so on. In brief, it’s less fun.
When using “theater of the mind” to run crunchy systems like D&D, though, the big problem is areas of effect. Who gets hit? Can you avoid hitting allies? Etc. So what I did, as a resource for myself at least, is I went through the various areas of effect I could find in the PHB and ran them through the formulas on page 249. Here are the results, with an added option of a random roll to determine targets:
|15’ arc (burning hands)||2 targets||1d4|
|15’ radius (darkness)||3 targets||1d6|
|30’ radius (auras)||6 targets||1d12|
|30’ cone||3 targets||1d6|
|60’ cone||6 targets||1d12|
|20’ radius (fireball)||4 targets||1d8|
|40’ radius (conjure volley)||8 targets||2d8|
|60’ radius (daylight)||12 targets||2d12|
|100’ line (lightning)||3 targets||1d6|
|10×10’ cubes (fire storm)||20 targets||2d20|
Did I miss an area of effect here? Did I forget something?
Hope these are helpful, mind-thespians!