The hail was as big as pea

خیلی ممنونم بابت پاسخ‌گویی، گفتم شاید pea واقعاً در اینجا اون معنی ساده تشابهی رو نداشته باشه 

You probably  know the size of a pea and the sentence is simply describing the size of that hail which was the same as a pea🫛

You may say it wasn't that big but you won't say the same thing when it hits your head