Sample size calculator
Most sample-size calculators written for Philippine theses implement one formula — Slovin's — and apply it to every study. Slovin's formula is valid in one specific situation: estimating a population proportion, at 95% confidence, with a known population size. Outside that, it answers a different question than the one you asked.
This one asks what you are estimating first, then routes to the method that answers it — and tells you plainly when Slovin's formula is not the right tool, with the source.
Why the formula matters more than the number
A panel asking how you arrived at your sample size is not asking for a figure. They are asking whether the figure follows from your design. That is why this calculator shows the formula it used and the values it used it with — so the answer is reproducible rather than asserted.
If you are comparing groups rather than estimating a single value, the question changes shape entirely: sample size then depends on the smallest difference worth detecting and the power you want, neither of which appears anywhere in Slovin's formula.