Can you convert kWh from monthly electricity meter readings to maximum demand kW or kVA?

Not really. at least not without more information. 3000kWh per month could be a steady 4kW load or 100kW for 1hr/day (approx). If you knew something about the kind of loads (e.g. continuous industrial process running 24x7 or simple offices open 8hrs/day 5days/week you might be able refine your guess a bit.

If you had half-hour readings, rather than monthly, you might be able to have a bit more confidence in your guesses - but you'd likely still need to know a bit about the nature of the loads - e.g. a few high-power but short duration loads (like an instantaneous electric shower) can still throw things out a lot.

   - Andy.

Not really. at least not without more information. 3000kWh per month could be a steady 4kW load or 100kW for 1hr/day (approx). If you knew something about the kind of loads (e.g. continuous industrial process running 24x7 or simple offices open 8hrs/day 5days/week you might be able refine your guess a bit.

If you had half-hour readings, rather than monthly, you might be able to have a bit more confidence in your guesses - but you'd likely still need to know a bit about the nature of the loads - e.g. a few high-power but short duration loads (like an instantaneous electric shower) can still throw things out a lot.

   - Andy.