It all depends on the ratio of how many calories you eat vs how many you burn. For every 3500 calories you eat that you don't burn, you gain one pound and you have to burn 3500 more than you eat to lose one. It's very difficult to measure how many you burn but understanding how it works helps. Look on the box the rice came in and it will list the calories.
I wouldn't worry about gaining a lot of weight from eating rice. Look at the people in countries where the principal diet is rice. You seldom see someone overweight. It's the cheeseburger, fries and shake culture that makes you grow horizontally.