How big is a large onion anyway? The picture below was taken of onions purchased on the same day at 3 different local grocery stores, each being the largest at their respective stores. It’s no wonder that home cooks have a hard time duplicating recipes. The variation between these onions is huge. While it may not have an impact on some dishes, it most certainly might have an impact on others. It’s the recipe’s fault for using a relatively inaccurate term for size when weight would have been a better choice.