We're lucky to live in an age where a wide variety of condoms are available to fit any size penis. There's plenty of advice on how to pick a proper size based on your girth, but how do you know that it's a proper fit? The only way to really know for sure is to give it a try.
The best description of a properly fitted condom is that it should be "snug". A condom of the right size will be easy to put on, won't have lots of wrinkles or air bubbles, and will only apply light pressure at the base. It's okay if it doesn't unroll all the way; most condoms are longer than most dicks and are designed to work just fine with material still unrolled at the base.
A properly fitting condom is hugely important for safe and successful sex. So it's important to get this right.
A condom that's too loose will have a lot of air trapped beneath, will wrinkle up with friction, or may easily slide or fall off. The last thing you want is to have to fish a used condom out of your partner.
Conversely, a too-tight condom poses different issues, including erection suppression, breaking, and loss of sensation.
The best way to test if the condoms you just bought are a good fit is to try them out. Get hard, apply a small amount of lube to your dick, and roll the condom on; it should go on easily, leaving the reservoir tip that many have at the end loose. Then there are two things to do:
- Gently grab on the tip and try to pull the condom off. It should generally stay in place and require a fair amount of pulling to dislodge.
- Lube up a hand and masturbate with the condom on — a lighter grip is recommended. It should mostly stay in place on your penis; some light wrinkling is acceptable, especially if you are not circumcised and have a more mobile foreskin. It's normal for sensation to be slightly reduced when wearing a condom (it is a layer between your penis and the world, after all), but you should still have most of your sensitivity.
If you can do both of those and the condom still stays in place then you have a good fit for use in penetrative sex. If the condom moves a lot independently of your dick's skin then you should consider a smaller size. If you're having trouble maintaining an erection or losing too much sensitivity then you might need to go bigger.