Is half a syringe enough? My main concern is my upper lip but I want more balanced lips for my face (Photo)

This will depend on the final results you want, but half a syringe may be enough. You may have swelling 1-2 weeks after lip fillers. I prefer to use a micro cannula to inject the lips to prevent bruising.
I hope this helps.

Hi and thanks for your question. Yes, half a syringe would most likely be enough for you. Your lips are not small, so for the very subtle enhancement that you sound like you are seeking, that will be fine. I would probably suggest a soft HA filler like Juvederm. Results are natural and soft to the touch with good duration at around 6 to 8 months. Hope that helps.

Dear lips1011,it depends on your  goals. Based on your photo, you look like a great candidate for lip augmentation. I typically use Juvederm for my lip sculpting. There are two main focuses of lip injections, adding volume and actually sculpting the shape. Both involve injecting the filler in different areas of the lips and patterns.
I would recommend finding a plastic surgeon to perform you lip injections. Most of my patients have results that last at least 6 months if done correctly.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery