This is Tyson a close up shot of the male beak the bit you need to pay attention to is the width just below the nostrils on males it is much wider than on hens as i will attempt to show you in the next picture.
This is Nemo a close up shot of the female beak again check out the difference in the width of the beak
This is Keiko another male beak. Again pay attention to the width, while in general the hens beak's are smaller in length it's not always the case, also please bear in mind the distance & angle's photo's are taken as that can have a bearing when trying to identify the sexes
This is Olive, Keiko's Mum so obviously a female but perhaps not so obvious for some. Never let it be said that photo sexing is easy it's not, the best way is 2 birds side by side & look for yourself if your keeping 1 as a pet though then you may have problems getting it accurately sexed.
This is Rocky Dad to Tyson & another example of a male, again careful to not be misled as to how much smaller in length his beak looks on this photo to perhaps some of the hens.
This Is Babe Partner to Rocky & mother of Tyson i personally think this is the best example here of a hen's beak both narrow and short in length
While attempting to show you the beaks and the differences here with the 6 photo's it occurred to me how different each one really looked. In reality that's probably true it's like trying to tell the sex of a human by just the nose, we all have different shapes and sizes and in truth it could probably not be done. But it is much different with a little experience, a little know how and 2 birds to compare, then even the novice breeder would be able to tell 95% of the time the sexes.
You are usually able to hazard a good guess of a chicks sex by 4 weeks old, but i won't commit until they are 8 weeks and are fully feathered, again comparing one chick to another does make this much easier.
There are other ways which with a keen eye and a little experience that can contribute to being able to sex your birds, Hens tend to have flatter heads than Cocks, and it is said that in the red crested, the hens crest is a deeper colour, not sure if I buy into that one though as I just don't see it in any of my birds.
The one sure way is D.N.A testing which really is not needed for breeders but for pet owners who have just got to know lol. That may be your avenue.
Also at this point it's worth me mentioning that both sexes will mate so Boy & Boy and Girl & Girl will go through the motions. Hens with a partner from around 4 months will participate in sexual activity (Mating) and that may be one of your best clues as the hen will omit a mating call, even single hens, so look out for this noise.
Here Are The Same Photo's Again In The Same Order As Above