A method for quantifying nucleic acid is provided. The method includes determining a first reference threshold cycle for a first predetermined input quantity for a reference nucleic acid, determining a first target threshold cycle for the first predetermined input quantity for a target nucleic acid, determining a second reference threshold cycle for a second predetermined input quantity for the reference nucleic acid, and determining a second target threshold cycle, by the processor, for the second predetermined input quantity for the target nucleic acid. The method further includes receiving a sample threshold cycle, determining a sample input quantity based on the first and second reference threshold cycle and the first and second target threshold cycle, and displaying the sample input quantity to a user.