At 400 degrees F, you should cook salmon for six minutes for each half-inch of thickness. So, if you have a quarter-inch fillet, you will just cook it for three minutes, flipping it after one and a half minutes. For a one-inch fillet, cook for a total of 12 minutes, six minutes on each side. To make sure it is completely cooked, use a meat thermometer. It should be 125 to 135 degrees F when it is done.