Here is the new formula discovered by BinText which is 100% accurate past round 12..
Number of zombies per round Single player =0.0842 * (R)^2 + 0.1954 * (R) + 22.05 2 Players =0.1793 * (R)^2 + 0.0405 * (R) + 23.187 3 Players =0.262 * (R)^2 + 0.301 * (R) + 33.114 4 Players =0.3462 * (R)^2 + 0.4964 * (R) + 43.164Replace 'R' with Row() Function in Excel to make this formula work.
EDIT:I promised I was going to update my previous chart and I finally did because the previous one was bit confusing to read. Let me know if you guys see any inconsistencies.
Here is the spreadsheet I uploaded recently which could be a good resource for those that are doing high rounds in solo.
Tested on Ascension.
Credit to DuckCall00 for directing me to http://denkirson.proboards.com website and & BinText for discovering this formula.