Sometime figuring out how much to pay when overtime is involved is tricky, especially when it is involving piece work. On the DOL website I found information that lays it out clearly as to how to calculate the overtime including examples:
Computing Overtime Pay
Overtime must be paid at a rate of at least one and one-half times the employee’s regular rate of pay for each hour worked in a workweek in excess of the maximum allowable in a given type of employment. Generally, the regular rate includes all payments made by the employer to or on behalf of the employee (except for certain statutory exclusions). The following examples are based on a maximum 40-hour workweek applicable to most covered nonexempt employees.

1. Hourly rate (regular pay rate for an employee paid by the hour) – If more than 40 hours are worked, at least one and one-half times the regular rate for each hour over 40 is due.

Example: An employee paid \$8.00 an hour works 44 hours in a workweek. The employee is entitled to at least one and one-half times \$8.00, or \$12.00, for each hour over 40. Pay for the week would be \$320 for the first 40 hours, plus \$48.00 for the four hours of overtime – a total of \$368.00.

1. Piece rate – The regular rate of pay for an employee paid on a piecework basis is obtained by dividing the total weekly earnings by the total number of hours worked in that week. The employee is entitled to an additional one-half times this regular rate for each hour over 40, plus the full piecework earnings.

Example: An employee paid on a piecework basis works 45 hours in a week and earns \$405. The regular rate of pay for that week is \$405 divided by 45, or \$9.00 an hour. In addition to the straight-time pay, the employee is also entitled to \$4.50 (half the regular rate) for each hour over 40 – an additional \$22.50 for the 5 overtime hours – for a total of \$427.50.
Another way to compensate pieceworkers for overtime, if agreed to before the work is performed, is to pay one and one-half times the piece rate for each piece produced during the overtime hours. The piece rate must be the one actually paid during nonovertime hours and must be enough to yield at least the minimum wage per hour.

1. Salary – The regular rate for an employee paid a salary for a regular or specified number of hours a week is obtained by dividing the salary by the number of hours for which the salary is intended to compensate. The employee is entitled to an additional one-half times this regular rate for each hour over 40, plus the salary.

If, under the employment agreement, a salary sufficient to meet the minimum wage requirement in every workweek is paid as straight time for whatever number of hours are worked in a workweek, the regular rate is obtained by dividing the salary by the number of hours worked each week. To illustrate, suppose an employee’s hours of work vary each week and the agreement with the employer is that the employee will be paid \$480 a week for whatever number of hours of work are required. Under this agreement, the regular rate will vary in overtime weeks. If the employee works 50 hours, the regular rate is \$9.60 (\$480 divided by 50 hours). In addition to the salary, half the regular rate, or \$4.80, is due for each of the 10 overtime hours, for a total of \$528 for the week. If the employee works 60 hours, the regular rate is \$8.00 (\$480 divided by 60 hours). In that case, an additional \$4.00 is due for each of the 20 overtime hours for a total of \$560 for the week.
In no case may the regular rate be less than the minimum wage required by the FLSA.
If a salary is paid on other than a weekly basis, the weekly pay must be determined in order to compute the regular rate and overtime pay. If the salary is for a half month, it must be multiplied by 24 and the product divided by 52 weeks to get the weekly equivalent. A monthly salary should be multiplied by 12 and the product divided by 52.