I presume you are making it yourself then with your own kefir grains? What I do is ferment about 16 oz milk (roughly 500 ml) into kefir and then pour that into a larger container in the fridge for storage. My container in the fridge holds about 50 oz so I keep about 3 batches in the fridge. In the fridge, the kefir undergoes a slower secondary fermentation which thickens it up. Stir with a wood spoon before serving. Once I get that container full, I'll drink about 16oz a day and then continually refill it up with new kefir I am making so it always stays roughly full.
Kefir making can be tricky, seasons impact how fast the milk ferments and if it over ferments the end product can be runny; it can also be runny if it under ferments. There is a definite Goldilocks thing going on with my kefir. Grains can grow rapidly at some times, you may have to cull some off and eat them or give them away since the milk can ferment too fast. I'll usually keep my grains in the 16oz fermenting container in the fridge over night, then take them out first thing in the morning to ferment from say 6 am to 8 pm. For now this works, but with my grains growing, I'll have to shorten the time, get rid of some grains, etc. I'm constantly rejiggering something in the kefir making variables.