more info bud, how much light are they getting? how long is your veg and flower cycle?
Key things though that i've learned since growing. Different strains produce different yeilds, you can have strains that produce lower yields, and others that produce lots more. Also be aware of the nutrients your using. If you want better results, consider trying different nutrients and different combinations and really work on getting your own feeding schedule really working for your strain. I found fox farm in the past to produce pretty average results for me. I get much higher yields with supernatural brand nutes instead. i highly suggest looking into them. Obivously theirs many other factors other than just nutes, consider your lighting too.