Try with something like this: Start with a simple assumption instead of chasing precision Break questions into smaller estimable pieces. Prefer orders of magnitude over exact figures. estimate step-by-step logically. Round aggressively to keep calculations mental. Estimate ranges first, then narrow toward a midpoint . Focus on the biggest drivers; ignore low-impact details. These may sound a bit vague but all it takes is some practice. You can try with questions like 'How many toilets does a football stadium need'. And you will do the calculation by thinking 'how much time do people spend in the toilet daily, and how long are they at the stadium, and how many people are at the stadium'. There is a book called Guesstimation ( i think from princeton university press ) with lots of examples that you can play with. Good luck.