What is an electrical load calculation?

An electrical load calculation totals the maximum expected demand (in watts or volt-amps) of all circuits in a panel or service entrance. It determines the minimum service size (e.g. 100 A, 200 A) and ensures the panel is not overloaded. NEC Article 220 provides the standard method for dwelling-unit load calculations.

How does the NEC demand factor work for residential loads?

The NEC allows demand factors to reflect the statistical reality that not all loads run simultaneously. For general lighting (NEC 220.42): 100% on the first 3,000 VA, 35% on the next 117,000 VA, and 25% on anything above 120,000 VA. Large appliances such as ranges use separate demand factors from NEC Table 220.55.

What loads must be included in a service calculation?

The required inventory depends on occupancy and the adopted calculation method. This tool only sums VA rows that you enter; it does not discover required loads, add occupancy allowances, classify equipment, or choose a service-calculation method.

How do I calculate the total electrical load for a house?

Use NEC Article 220 Standard Method: (1) General lighting = 3 VA × floor area in sq ft. (2) Add small-appliance and laundry loads. (3) Apply demand factors from NEC 220.42. (4) Add all fixed appliances at 100%. (5) Add HVAC at 100% of the larger of heating or cooling. (6) Divide total VA by service voltage (240 V) to get amps; round up to the next standard service size.

When do I need a 200-amp versus 100-amp service?

There is no safe equipment-list shortcut. Complete the adopted service calculation from verified loads and permitted demand factors, then consider standard equipment ratings, capacity, future additions, utility requirements, and local approval. This connected-load sum does not answer that question.

Is this electrical load calculator free?

Yes. The browser tool is a free connected-load summation aid: enter named VA rows and system voltage to see total connected VA and nominal current. It does not apply demand factors or recommend a service size.

What is the difference between connected load and demand load?

Connected load is the sum of all installed equipment nameplate ratings — the theoretical maximum if everything ran simultaneously. Demand load applies diversity/demand factors to estimate realistic simultaneous draw. Service and feeder sizing uses demand load; connected load is used for equipment ratings and fault-current calculations.

Can I use this calculator for residential or commercial service sizing?

Use it only to total a prepared connected-load list. Residential and commercial service sizing require different current adopted rules, classifications, demand factors, phase treatment, and project data; none are automatically applied here.

Connected Electrical Load Calculator — Free VA Total

Electrical lab bench with calculator, multimeter, oscilloscope, and low-voltage test circuit used to verify Electrical Load Calculator results. — Calculate the nominal result, then verify assumptions, limits, and real behavior with appropriate measurements.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 1 of 8 — Electrical Load Calculator input-to-result overview.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 2 of 8 — Formula and unit relationship.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 3 of 8 — Worked-example calculation path.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 4 of 8 — Input and assumption checklist.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 5 of 8 — Nominal result and interpretation.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 6 of 8 — Tolerance and worst-case verification.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 7 of 8 — Editable-circuit and related-tool next step.

Electrical Load Calculator formula, inputs, result, verification, or design-boundary visual 8 of 8 — Safety, model, and professional-review boundary.

Electrical load calculation workflow

An electrical load calculation turns an inventory of real loads into a documented design basis. Connected load is not automatically the same as demand load, service size, feeder current, energy use, or protective-device rating. The governing method depends on occupancy, load category, phase arrangement, utilization, demand/diversity rules, continuous operation, motors, heating/cooling, nonlinear loads, and local requirements.

Quantity	Formula	Use
Single-phase apparent current	I = VA ÷ V	Convert apparent load to nominal line current.
Three-phase apparent current	I = VA ÷ (√3 × VLL)	Balanced line-current estimate from line-to-line voltage.
Real power	P = V × I × PF, or √3 × VLL × I × PF	Relate watts, current, voltage, and power factor.
Energy	kWh = kW × hours	Estimate consumption; not conductor or breaker size.

Worked planning example

A balanced 18 kVA three-phase load at 400 V has a nominal current of 18,000 ÷ (√3 × 400) ≈ 26.0 A. If 18 kW were entered instead of 18 kVA, power factor and efficiency assumptions would be needed before current could be estimated. The release calculation must also address phase imbalance, continuous operation, harmonics, motors, demand rules, and the selected equipment.

Build a traceable load schedule

List each load with tag, description, phase, voltage, poles, watts or VA, power factor, duty, and source.
Normalize units without losing the source value.
Apply only the demand or diversity method permitted for the project.
Summarize per phase and flag imbalance or missing data.
Carry the reviewed result into the panel schedule, feeder calculation, and release package.

What this result does not prove

The calculator does not establish code compliance, protective-device coordination, available fault current, voltage drop, conductor derating, harmonic heating, generator performance, transformer inrush, or equipment suitability. Verify the governing rules through the applicable authority and current primary sources such as NFPA 70 through NFPA LiNK.