The TradesCalcPro Ohm’s & Watt’s Law Calculator is designed to help electricians, technicians, and students quickly solve electrical relationships between voltage (V), current (I), resistance (R), and power (P).
By entering any two known values, the calculator automatically determines the others using the foundational equations of circuit theory — saving time, improving accuracy, and helping verify work before installation or troubleshooting.

Ohm’s Law and Watt’s Law are essential for almost every aspect of electrical work, from calculating circuit loads and sizing conductors to estimating power usage and system efficiency.
This calculator simplifies those relationships while maintaining precision suitable for both field use and classroom learning.

Ohm’s Law:
Defines the relationship between voltage, current, and resistance.

1. V = I × R  (Voltage = Current × Resistance)
    
2. I = V ÷ R  (Current = Voltage ÷ Resistance)
    
3. R = V ÷ I  (Resistance = Voltage ÷ Current)
    

Watt’s Law:
Defines the relationship between power, voltage, and current.

1. P = V × I  (Power = Voltage × Current)
    
2. V = P ÷ I  (Voltage = Power ÷ Current)
    
3. I = P ÷ V  (Current = Power ÷ Voltage)
    

Combined Ohm’s and Watt’s Relationships:
By substituting Ohm’s Law into Watt’s Law, we can calculate power using resistance or current alone.

1. P = I² × R  (Power = Current² × Resistance)
    
2. P = V² ÷ R  (Power = Voltage² ÷ Resistance)
    

• Units used:
  • Voltage (V) in volts
  • Current (I) in amperes (amps)
  • Resistance (R) in ohms (Ω)
  • Power (P) in watts (W)