i have a plant about 1 foot i have to flower it becuase i dont have the time to let it get bigger shes about 1 month old she is a regular strain,but my first question is i heard they grow at least twice as high during flowering and how much yield should i expect im using hps lights

depending on the wattage of your hps, and the strain, and growing method. i wouldnt expect more than 1 oz. and yes a plant can double and in rare cases triple in height during flowering

1 oz damn i didnt expect that,i expected maybe a quarter little over a dime maybe,but oz would be nice