Panel Capacity Calculator

Formula used

• Apparent power per circuit: VA = (Watts × Qty) ÷ PF
• Continuous adjustment: VAadj = VA × ContinuousMultiplier (only for marked loads)
• Total adjusted load: VAtotal = ΣVAadj × DemandFactor × (1 + FutureAllowance)
• Panel capacity: VAcap = V × A (single-phase) or VAcap = √3 × V × A (three-phase)
• Equivalent panel current: Aeq = VAtotal ÷ (Factor × V), where Factor = 1 or √3
• Utilization: Util% = VAtotal ÷ VAcap × 100

How to use this calculator

1. Enter the panel phase, voltage, and main breaker rating from the nameplate.
2. Add each circuit load in watts, plus voltage, phase, and quantity.
3. Mark continuous loads and set your continuous multiplier as required.
4. Apply demand factor and future allowance to match your project assumptions.
5. Click Calculate capacity to see utilization and headroom.
6. Use Download CSV or Download PDF for records.

Professional notes for panel capacity checks

1) Capacity is more than “breaker size”

A main breaker rating (for example, 100 A, 200 A, or 400 A) sets an upper limit, but usable capacity depends on voltage system and load type. This calculator converts each circuit into volt‑amps (VA) using watts and power factor, then applies a continuous‑load adjustment. That mirrors common design practice where long‑duration loads are treated more conservatively.

2) Voltage and phase change the kVA picture

For single‑phase 120/240 V panels, the capacity estimate uses the service voltage you select. For three‑phase panels (often 208/120 V or 480/277 V), capacity is driven by kVA = √3 × V × A ÷ 1000. A 200 A panel at 208 V three‑phase has a different kVA ceiling than a 200 A panel at 240 V single‑phase.

3) Continuous loads and the 125% approach

If a load is expected to run for extended periods, many codes and specifications apply a 125% factor. The calculator implements this by dividing continuous VA by 0.80, which is equivalent to multiplying by 1.25. This helps prevent designs that “pass on paper” but trip under sustained operation.

4) Demand, diversity, and real construction schedules

Construction projects rarely hit peak load on every circuit at the same time. Lighting may be continuous while receptacles are intermittent; HVAC can be seasonal; temporary power can shift week to week. Use the optional demand factor to model diversity (for example, 0.70 to 0.90) and compare scenarios before committing feeder sizes or panelboards.

5) What the report is best for

The CSV/PDF export is useful for submittals, internal reviews, and quick coordination between electrical, mechanical, and site teams. Treat results as an engineering estimate; verify final compliance with the governing code, manufacturer data, and stamped design documents for your jurisdiction.

FAQs

1) Does this replace a full load calculation?

No. It provides a structured estimate from entered loads. Final sizing should follow your applicable electrical code, stamped drawings, and manufacturer limits for bus rating, breakers, and temperature.

2) Why do you ask for power factor?

Some equipment draws more apparent power than real watts. Power factor converts watts to VA so the panel and feeder loading reflects current draw more realistically, especially for motors and drivers.

3) What if I don’t know the power factor?

Use a conservative default (like 0.90) for mixed loads. For motors, VFDs, or LED drivers, check nameplates or submittals to improve accuracy.

4) How is a continuous load handled?

When you mark a circuit as continuous, the calculator applies a 125% style adjustment by dividing the circuit VA by 0.80 before summing totals.

5) What demand factor should I use?

Typical conceptual ranges are 0.70–1.00. Use 1.00 for worst‑case. Use a lower factor only when diversity is justified by the project schedule, occupancy, and equipment duty cycle.

6) Why does three‑phase use √3?

In balanced three‑phase systems, total power relates to line voltage and current through √3. This is standard in kVA calculations for panel and feeder loading.

7) What counts as “panel capacity” here?

Capacity is estimated from the selected voltage system and main breaker rating, then compared to calculated VA demand. It does not automatically validate conductor ampacity, fault ratings, or breaker compatibility.

Example data table