Why your fund isn't your neighbour's
The right emergency fund doesn't come from a fixed rule, but from looking at your life: how long it would take you to get back to normal if things went wrong. That's why this calculator starts from your essential expenses (not your total spending) and adjusts the months for three factors that genuinely move the figure: your income stability, whether you rely on one or two salaries, and whether you have dependents.
The more unpredictable your income and the more people depend on you, the bigger the cushion you need. If you have very stable employment, two salaries at home and no dependents, the low end of the range is enough.
To go deeper, read the article Emergency Fund: How Much You Really Need Based on Your Situation.