The perpetual "upper middle class/middle class/upper class" altercation is Cr.ap.

This portal has a wonderful HH income (albeit 2014) percentile comparator.
://.salary.sg/2014/compare-your-household-income-2014/
Please use it. Caveat - you just take GROSS Annual HH (incl employer cpf) and divide by 12.

If we adopt Pew research definition of middle class, it is from 2/3 of median HH income to twice the Median HH income. If you want to use other definitions, just state your income percentile thresholds.