Ours period underwear are generally standard in size and correspond to most underwear you already have in your drawer. You must always choose a size that fits - this helps prevent bleeding. 

⭐︎ Panties in cotton will be more stretchy in the fabric than panties in mesh. 
⭐︎ Feedback on this style is that it is large in size. Feel free to take a size smaller than you usually do. 

Here are measures of Period flow Brief - high waist (cotton). 
To compare, lay a pair of your own panties flat on a table and measure them hip to hip.