3 inches is a good sized Serrano
I usually go by color. I pick them when they turn red and make a hot sauce from them but they are just as good when green for salsas and other dishes that need some heat.
Should have quite a bit more punch than a jalapeno.
taste one
if you like it pick them
but leave some and see how they taste as they mature a bit more.
good luck
probably my favorite pepper. I grow about a dozen plants and they're usually very prolific but as with most things in the garden this year it wasn't as productive as in years past.

Thank you darthweeder :) my bf bought me the plants, I think one is turning red, and some look like they have dark purple on them

serano is very similar in size, shap, taste to jalapano.
A lot of times I cannot tell the difference.

i love serreno peppers. they do pack more punch then the jalapeno.

one catalog rated jalapenos at 5.5 and cayenne at 8.5 on a 10 heat scale. however not all cayenne or any other kind are equal in heat. the serrano is some where between the cayenne and the Jalapeno. i like the serrano because it taste better and is easier to dry.

i also like my pepper of any kind after they are ripe. the serreno will turn bright fire engine red.

well now i have told you all i know about serreno peppers so now you know i don't know a lot.

i am currently eating a raw salsa made with one ripe cayenne and one ripe jalapeno. with opalka tomatoes, a walla walla onion and a ripe yoyo bell pepper.

you can tell i am a gringo because i have to stop and let my mouth stop hurting before i go after it again.

Dean

hope you dont mind me jumping on this thread, I have a similiar question. I planted jalopena's, serrano's and habanero's. For whatever reason, I thought the serrano's and the hab's were more similiar in size, (that is til I read this thread). The markers I put up are not readable :(
and I have more of the smaller thinner ones (the jalapeno's to me were easy to identify, they are bigger and wider.

other than tasting them, (not wanting to light up) how will I be able to tell?

I don't think Jalapenos and Serranos look similar. Serranos are about the same length as Jalapenos but much skinnier. The Serranos will be hotter, too. Habaneros (depending on the type) turn orange when ripe and have more of a shield shape (square with the bottom end pointed). Habaneros will be even hotter than the other two.