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Calculate total electrical load in watts and amps, find required circuit breaker size, and check NEC 80% loading rule for any combination of household or commercial appliances. Essential for electrical panel design.
Electrical load calculations determine the total current demand on circuits and panels. NEC (National Electrical Code) requires circuits to be loaded to no more than 80% of breaker rating for continuous loads. Accurate load calculations prevent overloaded circuits, tripped breakers, and fire hazards from undersized wiring.
| Appliance | Wattage | Notes |
|---|---|---|
| LED bulb | 8-10 W | 1800 lm, replaces 100W incandescent |
| Refrigerator | 150-400 W | Energy Star: 150W, old: 400W |
| Air conditioner (1-ton) | 900-1200 W | 12,000 BTU cooling |
| Electric water heater | 4000-4500 W | 40-50 gal tank |
| EV charger (Level 2) | 7200 W | 240V, 30A circuit |
| Microwave | 700-1200 W | Typical home microwave |
| Clothes dryer | 5000-5500 W | 240V, 30A circuit |
This free engineering calculator uses established formulas from mechanical, civil, electrical, and chemical engineering. Results are computed instantly in your browser with no data sent to any server. For professional engineering applications, always verify calculations independently and have results reviewed by a qualified engineer. Use the Copy button to save results and Share to send this calculator to colleagues.
Electrical load calculations are required by the National Electrical Code (NEC) for service entrance sizing, panel board design, and branch circuit design. The NEC specifies minimum load requirements for dwelling units, commercial occupancies, and industrial facilities. Actual demand rarely equals connected load — demand factors account for the fact that not all loads operate simultaneously at full rated power.
| Load Type | NEC Requirement | Notes |
|---|---|---|
| Lighting (general) | 3 VA per sq ft | Dwelling units |
| Small appliance circuits | 1500 VA each | Minimum 2 circuits in kitchen |
| Laundry circuit | 1500 VA | One required in dwelling |
| Demand factor (lighting) | 35% of load above 3000 VA | NEC Table 220.42 |
| Motor loads | 125% of FLC | Largest motor x 1.25 |
| Electric heat | 100% of total | No demand factor |
| Wire Size | Max Breaker | Typical Application |
|---|---|---|
| 14 AWG | 15A breaker | General lighting, outlets |
| 12 AWG | 20A breaker | Kitchen circuits, garage |
| 10 AWG | 30A breaker | Dryer, water heater, AC |
| 8 AWG | 40A breaker | Large AC units, cooktop |
| 6 AWG | 50-55A breaker | EV charger (50A), range |
| 4 AWG | 60-70A breaker | Subpanel, large loads |
Single-phase (120V/240V): standard US residential. Most household appliances. Two-wire (120V) for lighting and small appliances. Three-wire (240V) for heavy appliances. Three-phase (208V/480V): commercial and industrial. More efficient for large motors. 3-phase power = sqrt(3) x V_line x I_line x PF = 1.732 x V x I x PF. Three-phase motors are more efficient and smoother than single-phase for the same power output.
Engineering calculations are the foundation of every designed system — from the bolts holding a bridge together to the pipe carrying water to your tap. These free calculators cover the most commonly needed engineering formulas across civil, mechanical, electrical, and chemical engineering disciplines. All calculations use standard SI units and established engineering formulas from recognized references.
Engineering design always includes safety factors to account for material variability, load uncertainty, construction tolerances, and progressive deterioration. Typical safety factors: structural steel bending 1.67 (ASD), concrete compression 1.5-2.0, bolts in tension 2.0-3.0, pressure vessels 3.5-4.0. Always verify that your design complies with applicable local codes, national standards, and industry regulations before construction or installation.
Engineering is both a science and a craft. Formulas provide exact answers when inputs are exact — but real engineering involves estimating loads, assuming material properties, and accounting for construction tolerances. The best engineers know which simplifications are conservative (on the safe side) and which might be unconservative, and they apply appropriate margins accordingly.
Supplement these calculators with free engineering references: AISC Steel Construction Manual (steel design), ACI 318 (concrete design), NFPA 70 NEC (electrical), ASHRAE Fundamentals Handbook (HVAC), and Machinery Handbook (mechanical). Engineering toolboxes, NIST databases, and professional society websites provide free access to many standards and reference materials for non-commercial educational use.