Amp Draw Calculator

How to Use This Calculator

Calculate total amperage to ensure your circuits aren't overloaded:

1. List all devices that will be on the circuit.
2. For each device, enter either the wattage (from the label) or the amp rating.
3. If entering wattage, select the circuit voltage (120V or 240V).
4. Add all devices that could run simultaneously on this circuit.
5. Click 'Calculate' to see total amp draw and whether it's within safe limits.

Why This Matters

Every circuit has a maximum amperage capacity determined by the wire gauge and breaker size. Exceeding this capacity causes breakers to trip at best, and can start fires at worst. When adding new devices to a circuit - especially high-draw items like space heaters, air conditioners, or power tools - you need to know if the circuit can handle the additional load. This calculator helps you add up all the loads to ensure safe operation.

• Prevent circuit overloads and breaker trips
• Determine if a circuit can handle additional loads
• Plan new circuits with adequate capacity
• Identify circuits that are close to maximum capacity
• Calculate loads for generator sizing

Worked Examples

Common Mistakes to Avoid

• Forgetting that some devices have higher startup (inrush) current than running current - motors especially.
• Adding up nameplate ratings without considering actual simultaneous use - not everything runs at once.
• Ignoring the 80% rule - continuous loads should use only 80% of circuit capacity.
• Not accounting for 'hidden' loads on a circuit like bathroom exhaust fans or always-on devices.
• Using peak wattage instead of typical running wattage for calculations.