How many calories in one gram of fat? One gram of fat has 9 calories. About 30 – 35% of your calories come from fat. Body uses fat as a fuel, to build nerve tissue and hormones. We all require certain amount of fat to fuel to for the growth and other activates of our body. But if the amount of fat consumed is greater than the amount used for the above then they are stored in the body as fat cells. As fat cells accumulate the person tends to gain weight.