You mean the length that the actual episodes that a show usually has? Well discounting opening/ending credits and obviously the space to put commerical breaks in, I would say around 19-20 minutes nowadays. Commericals always take up at least a solid 8 minutes and you typically have 7-6-7 minute type breaks or 10-10 minute type breaks for shows. May also depend the network you're targetting for as well since each one has they're own standard, but I'd say no lower then 18 minutes and no higher then 23-25 minute episodes is the overall standard. Hope that helps out.