House Wiring Load Calculator

Step-by-Step Guide

1. 1Add Your Appliances: Click Add Appliance for each device in the home, or start from the Appliance Library for common presets like LED bulbs, ceiling fans, and air conditioners with typical wattage filled in.
2. 2Enter Quantity and Wattage: For each appliance row, enter the quantity and wattage per unit, checking the nameplate for accuracy. The calculator multiplies quantity by wattage automatically.
3. 3Select Your Supply Voltage: Choose 120V, 240V, 230V or 220V to match your electrical system, since current equals power divided by voltage.
4. 4Set the Diversity Factor: Adjust the slider between 0.5 and 1.0 to reflect realistic simultaneous usage. 0.7 to 0.8 is standard for typical residential homes.
5. 5Read the Total Load and Breaker Recommendation: The calculator shows total connected load, adjusted load, current in amperes, apparent power in VA, and the recommended standard breaker size with a 1.25x safety margin.
6. 6Save, Export, or Start From a Preset: Apply Small Apartment, Medium House, or Large House presets as a starting point, then save to history or export a CSV or text report.

What This Tool Provides

• ✓Real-time calculation as you edit appliances
• ✓34-item appliance wattage library across 9 categories
• ✓Three house-size presets: Small Apartment, Medium, Large
• ✓Support for 120V, 230V and 240V systems (and legacy 220V)
• ✓Adjustable diversity factor slider (0.5–1.0)
• ✓Standard breaker size recommendation with 1.25x margin
• ✓Apparent power (VA) output for panel sizing
• ✓Full step-by-step calculation shown for every result
• ✓Calculation history (last 20 entries)
• ✓Export results as CSV or text report
• ✓Private: your inputs are not collected or stored
• ✓No registration required

Pro Tips

• 💡Check the actual nameplate wattage on your appliances rather than relying solely on the library defaults. A specific refrigerator model can range from 150W to 400W depending on size and efficiency rating — the library value of 300W is a reasonable starting estimate, not a substitute for the real number.
• 💡Use a diversity factor of 0.7–0.8 for typical residential planning, but consider 0.9–1.0 for homes with heavy simultaneous usage patterns, such as a house running central AC, an electric range, and an EV charger at the same time during summer evenings.
• 💡Give dedicated circuits to high-wattage single appliances like water heaters, electric ranges, and AC compressors — these should generally be calculated and breakered separately from the general diversified household load rather than folded entirely into one aggregate number.
• 💡Add 20–25% headroom to your final calculated load if you're planning a panel for a home you expect to add appliances to later — an EV charger, a hot tub, or a home addition. Upgrading a panel later is far more expensive than sizing it correctly the first time.
• 💡Remember that motor-driven appliances like air conditioners and refrigerator compressors draw a brief inrush current at startup that's several times their running wattage. This calculator uses steady-state wattage, so breaker trip curves (not just average current) matter for circuits with multiple motor loads starting together.
• 💡Cross-check your calculator result against your electrical panel's main breaker rating before assuming you have spare capacity. A 100A panel with an existing 7,148W adjusted load at 240V (29.8A) still has meaningful headroom, but always verify the panel's labeled rating, not just an assumption.

Common Mistakes to Avoid

• ✕Don't leave the diversity factor at 1.0 for routine residential sizing. This models every appliance running full-tilt simultaneously, which almost never happens in practice and results in an oversized, more expensive panel and service entrance than the home actually needs.
• ✕Don't select the wrong voltage for your region. Entering 120V for a 230V European household (or vice versa) doubles or halves the calculated current and produces a breaker recommendation that's wrong by roughly a factor of two — always confirm your panel's labeled system voltage first.
• ✕Don't forget to include large, occasional-use appliances like clothes dryers (up to 3000W), electric ovens (2000W), and window AC units when estimating total load. Omitting even one high-wattage appliance can understate your total connected load significantly.
• ✕Don't treat this calculator's output as a substitute for a code-compliant load calculation on a permitted job. This tool uses a simplified diversity-factor method for planning; formal permit submissions typically require a jurisdiction-specific method like NEC Article 220 with category-specific demand factors, performed by a licensed electrician.
• ✕Don't apply the same 1.25x safety factor logic to interpret this as the maximum safe continuous draw on the recommended breaker. The 1.25x factor sizes the breaker to the calculated load; it does not mean you can safely run 125% of your original calculated current through that circuit indefinitely.