You may be familiar with the formula BTUH = CFM x ΔT x 1.08. This same formula is often rearranged to use for determining airflow by measuring the heat input and temperature rise.
CFM=BTUH/( ΔT x 1.08)

To get the BTU per hour (BTUH) with electric strips you use the formula:
BTUH = volts x amps x 3.41 BTUH/watt