I'm 5ft 4 and i weigh 140 pounds. how many calories would i equire in a day if i want to lose a stone?

Depends: On what you eat and burn now! you should strive for about 2 pounds per week for a healthy and sustainable weight loss. Depending on your caloric needs now (what your body burns based on job, lifestyle, and activity--everybody is different), you should reduce intake by about 10% and increase (or start) exercise as well. Gradual loss is healthy; rapid loss is not, and cannot be maintained either!