Drag is directly proportional to velocity squared. Hence Drag=C * V^2 where c is a constant and v is the velocity of the body relative to the fluid. The usual form is Drag=1/2 CpAv^2. Where C is the drag coefficient, p is the Greek letter rho representing the density of the fluid and A the effective cross sectional area.
Note: Before just asking for a formula try google or wikipedia in future.