Circuit Load Calculator
Calculate total load and available capacity on a circuit
Circuit breaker rating
120V or 240V
Total watts already on circuit
Watts of new device
Total Load
—
watts
Total Current
—
amps
Safe Capacity (80%)
—
watts
Can Add Load?
—
How to Use This Calculator
Our calculator helps determine if your circuit has capacity for additional loads.
- Check circuit breaker size
- Add up existing loads
- Enter wattage of new device
- If load > 80% limit, use separate circuit
AI Insights
Smart analysis for your project
Smart Estimates
Our AI cross-references material costs, regional pricing, and project complexity for more accurate estimates.
Waste Optimization
AI-calculated waste factors based on project type, not flat percentages. Saves 5-15% on material costs.
Best Practices
Recommendations derived from building codes, contractor data, and thousands of completed projects.
Calculation Formula
Total watts = Existing + New load
Total amps = Total watts / Voltage
Safe capacity = Breaker x Voltage x 0.80
Frequently Asked Questions
What is the 80% rule for circuits?
NEC requires continuous loads not exceed 80% of circuit rating. A 20-amp at 120V has safe capacity of 1,920 watts.
How many outlets on a 20-amp circuit?
NEC does not specify a maximum. Practical limit is 10 outlets for a 20-amp circuit.