The single most common mistake when buying anything that holds a miniature is assuming the model's stated scale describes its base. It almost never does. A model sold as "28mm" is describing an approximate height convention, and the disc it stands on might be 25mm, 28.5mm, 32mm or 40mm depending on when it was made and who made it.
Measure the base, not the model
For a round base, measure straight across the centre from one outside edge to the opposite outside edge, including the full bevel. Do not measure the raised inner platform — that is smaller than the footprint the model actually occupies. For an oval base you need two numbers: the shorter width and the longer length.
Do it without a ruler
Our base size checker does this two ways. On screen, you calibrate the page against a standard bank card and hold the base up against the outline. On paper, it prints an A4 sheet at exact size with a 100mm verification line so you can confirm your printer has not rescaled anything.
Once you know the number
Base size is the input almost every other decision depends on. Feed it into the display stand finder to see which stands physically fit and how many you would need, or into the scale and shelf-clearance calculator if you are working out whether a finished model will clear the shelf above it.
Every tool in the set is free and needs no account. You can see the rest on the WarSplay tools page.