A well pump has to meet your busiest hour, not your average day. Size it from the list of fixtures that run together, then check the well's yield against the pump you are considering. Do not start from a catalog model.
List the fixtures
Write down every water use on the property: each shower, each tub, each kitchen tap, the washing machine, the dishwasher, any outdoor hose, and any irrigation or livestock supply. Next to each one, note the flow rate from the fixture's labeling or the manufacturer's manual. Then mark the uses that tend to overlap in your busiest hour, such as a morning shower while the washer fills.
Set the peak
Add the flow rates of the uses that overlap in your peak hour. That total is the minimum flow the system should deliver at working pressure. A household where bathing and laundry often overlap needs a different pump from one where they rarely do. Ask your installer to show the peak calculation on paper.
Check the well
A pump can only deliver what the well yields over time. Ask for the well log, which records the depth, the static level, and the yield noted at drilling. Confirm the pump setting leaves a margin above the bottom of the well. If the log is missing, ask for a yield test before you commit to a larger pump.
Size the pressure tank
The pressure tank holds a reserve of water and pressure so the pump does not start and stop with every tap. Frequent starts are hard on any pump. Ask the installer how the tank volume was chosen against your peak draw and what cycle rate the design aims for. Write the answer into the proposal.
Ask for the written sizing
Before you sign, ask for one document that holds the sizing sheet, the well log reference, the pump model, and the tank volume. Compare it with what the installer described on the phone. If the sizing sheet is missing, the pump is being chosen by estimate, and you should ask again before anyone starts the work.