This is a script you can run on apache servers to help calculate MaxRequestWorkers/ServerLimit based on available free memory.

apache-prefork-tune.sh

#!/bin/bash

echo -e "\n*** Memory Output ***\n"

free -m

echo -e "\nEnter the amount of free memory (in MB), followed by [ENTER]:"

read FREE

ps -G www-data -ylC apache --sort:rss | awk -v free="$FREE" '{ s += $8; } END \
  { print "\nAverage Size:", s/(NR-1)/1024, "MB\n Num Servers:", NR-1, \
  "\n Total Usage:", (s/(NR-1)/1024)*(NR-1), "MB\n Max Servers:", \
  free/(s/(NR-1)/1024) }'