There isn't just one way to measure the size of a volcano.
Researchers and geography resources may consider:
Surface area
Volume
Elevation
Height
Base-to-summit relief
Geological structure

These measurements can produce different comparisons between volcanoes.
Learn more about
largest volcano explained and why the definition of “biggest” matters when comparing volcanic formations.
https://thecampusreview.com/geography/biggest-volcano-in-the-world/