Measure months of essential costs, not months of spending
The target should cover what you must pay, not what you normally pay. Housing, utilities, food, transport, insurance, minimum debt payments and childcare are in. Holidays, subscriptions and discretionary spending are not, because in the scenario you are preparing for, those stop.
This usually makes the target meaningfully smaller than people expect, which is the difference between a goal that gets started and one that does not.
Let your income volatility set the multiple
A salaried employee in a stable sector with a working partner is in a very different position from a sole trader whose income swings by half between quarters. The first can reasonably sit at the low end of the range. The second should be at the high end, or beyond it.
Notice periods, how quickly your skills are rehired, and whether a single event could remove both incomes in a household all pull the number in one direction or the other.
The first milestone matters more than the final one
A full six-month fund takes years for many people. A one-month buffer takes a season, and it is the increment that stops a flat tyre becoming credit card debt. Treat the first month as the real goal, then keep going.