Because the word small conjures many different ideas of size and space, let's just say, it's what feels right to you.
I've performed ceremonies with as little as 5 people in attendance, and that includes me!
Other weddings have been lovely affairs, all dressed up just like in the Bridal magazines, just pulled off on a smaller scale, say 20 - 30 guests. Depending on the chosen venue, you can factor in more people if there is outside space.
Whether jeans and a hoodie are your chosen attire on your wedding day, or a full length white gown with a bouquet of flowers, if you are happy, that's all that really matters.
Remember, your wedding day is just a one-day event, while your marriage is a long-term engagement.