CalcElectrical Panel Calculator
Last updated: 2026-08-10
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| Contracted power (kW) (kW) | Diversity factor | |
|---|---|---|
| Piso small (3.45 kW) | 3.45 kW | 0.5 |
| Vivienda estándar (5.75 kW) | 5.75 kW | 0.6 |
| Vivienda equipada (9.2 kW) | 9.2 kW | 0.7 |
| Local comercial (20 kW) | 20 kW | 0.8 |
| Nave industrial (50 kW) | 50 kW | 0.9 |
Planning an electrical installation requires careful calculation to ensure safety and efficiency, and the Electrical Panel Calculator is a free online tool that simplifies this critical task. This calculator quickly determines the maximum current, the recommended circuit breaker size (ICP), and the number of estimated circuits for your electrical panel, using just three key inputs.
What the Electrical Panel Calculator Does and When to Use It
The Electrical Panel Calculator is designed for electricians, engineers, homeowners, and anyone involved in designing or upgrading electrical systems. It takes the guesswork out of panel sizing by converting your total connected power into actionable data. You simply enter the total power in kilowatts (kW), the system voltage (typically 230V for single-phase or 400V for three-phase), and a simultaneity factor (the percentage of loads likely operating at once). The calculator then outputs three essential figures:
- Maximum Current (Imax): The highest current the system will draw under your given load conditions, measured in amperes (A).
- Recommended ICP (Circuit Breaker Size): The standardized rating for the main disconnect or general overcurrent protection device (available sizes: 16A, 25A, 32A, 40A, 50A, or 63A).
- Estimated Number of Circuits: The approximate number of 16A circuits needed to distribute the current safely, helping you plan your panel layout.
Use this calculator when designing a new home or office panel, upgrading an existing service, or verifying that your planned electrical loads are within safe limits. It is particularly helpful during the initial planning phase to avoid undersized panels or overloaded circuits.
Formula Explained Variable by Variable
The calculator uses a straightforward yet powerful formula based on Ohm’s Law and power calculation principles. Here is the breakdown of each variable:
| Variable | Meaning | Unit | How It Works |
|---|---|---|---|
| P | Total Power (potencia_kw) | Kilowatts (kW) | The sum of all connected loads you expect to run. The calculator multiplies this by 1000 to convert to watts (W). |
| V | System Voltage (tension_v) | Volts (V) | The line-to-neutral or line-to-line voltage. The calculator uses 230V for single-phase calculations and switches to 400V (with a factor of √3) for three-phase systems. |
| fs | Simultaneity Factor (factor_simultaneidad) | Decimal (0 to 1) | Accounts for the fact that not all devices run at full power simultaneously. A typical residential value is 0.7, meaning 70% of loads may be active at once. |
| Imax | Maximum Current | Amperes (A) | Calculated as: (P × 1000 × fs) / (V × factor). The factor is 1 for single-phase (V=230) or √3 (≈1.732) for three-phase (V=400). The result is rounded to one decimal place. |
| ICP | Recommended Circuit Breaker Size | Amperes (A) | Selects the next standard breaker rating above Imax (16, 25, 32, 40, 50, or 63A). For example, if Imax is 27A, the calculator picks 32A. |
| RITI | Estimated Number of Circuits | Count | Calculated as ceil(Imax / 16), rounding up to the nearest whole number. This assumes 16A as the standard circuit rating. |
Two Worked Examples with Real Numbers
Example 1: Single-Phase Home Installation (230V)
Scenario: You are wiring a small apartment with a total load of 8 kW. The system voltage is 230V single-phase, and you estimate a simultaneity factor of 0.7 (because not all appliances run at once).
- Inputs: P = 8 kW, V = 230 V, fs = 0.7
- Convert power to watts: 8 kW × 1000 = 8000 W
- Calculate maximum current: Imax = (8000 × 0.7) / (230 × 1) = 5600 / 230 ≈ 24.35 A, rounded to 24.4 A
- Choose ICP: The next standard breaker above 24.4A is 25 A
- Estimate circuits: RITI = ceil(24.4 / 16) = ceil(1.525) = 2 circuits
Result: You need a 25A main breaker and plan for at least 2 circuits (e.g., one for lighting and one for outlets).
Example 2: Three-Phase Commercial Installation (400V)
Scenario: A small workshop has equipment totaling 30 kW, running on a 400V three-phase supply. Because several machines may run simultaneously, use a simultaneity factor of 0.85.
- Inputs: P = 30 kW, V = 400 V (three-phase detected), fs = 0.85
- Convert power to watts: 30 kW × 1000 = 30000 W
- Calculate maximum current: Imax = (30000 × 0.85) / (400 × √3) = 25500 / (400 × 1.732) = 25500 / 692.8 ≈ 36.81 A, rounded to 36.8 A
- Choose ICP: The next standard breaker above 36.8A is 40 A
- Estimate circuits: RITI = ceil(36.8 / 16) = ceil(2.3) = 3 circuits
Result: A 40A three-phase main breaker is required, and the panel should accommodate at least 3 circuits (e.g., separate circuits for heavy machinery, lighting, and general outlets).
Common Mistakes When Using an Electrical Panel Calculator
Avoid these frequent errors to get accurate and safe results from the Electrical Panel Calculator:
- Entering power in watts instead of kilowatts. The calculator expects kilowatts (kW). If you have 5000 W, enter 5 kW, not 5000. This mistake can produce currents that are 1000 times too high.
- Using the wrong voltage for your system type. Single-phase systems typically use 230V (common in residential setups), while three-phase uses 400V. Entering 400V for a single-phase system will significantly underestimate the current, risking undersized breakers.
- Ignoring the simultaneity factor. Setting fs to 1 (100%) assumes every load runs at full power simultaneously. This is unrealistic for most installations and leads to oversized panels and unnecessary costs. Use a realistic factor (0.6–0.8 for residential, 0.7–0.9 for commercial).
- Forgetting to round up the ICP. The calculator automatically selects the next standard breaker size, but beginners sometimes try to use a breaker rated below the calculated Imax, which violates electrical codes and creates a fire hazard.
- Misinterpreting the estimated circuit count. The RITI value (circuits estimated) is a minimum guideline based on 16A circuits. If your actual loads require higher-rated circuits (e.g., 20A or 32A for heavy appliances), you must adjust your panel layout accordingly.
Frequently Asked Questions (FAQ)
Can I use the Electrical Panel Calculator for both single-phase and three-phase systems automatically?
Yes. The calculator detects the system type based on the voltage you enter. If you input 230V, it treats the system as single-phase and uses a factor of 1. If you input 400V (or any value above 230V), it switches to three-phase mode and applies the √3 factor for line-to-line voltage calculations. Simply enter your correct voltage, and the formula adjusts automatically.
What if my calculated maximum current falls exactly at a standard breaker rating, like 40A?
The calculator selects the next standard size that is greater than or equal to the Imax. For example, if Imax is exactly 40.0 A, the ICP recommended will be 40 A. This follows standard practice—a breaker should be rated for at least the full-load current. However, always verify with local electrical codes, as some regulations require a margin (e.g., a 125% safety factor for continuous loads).
Do I still need a licensed electrician after using this calculator?
Absolutely. The Electrical Panel Calculator is a powerful planning tool that gives you a reliable starting point for panel sizing and circuit estimation. It does not replace professional judgment, on-site inspection, or compliance with local electrical codes (such as NEC, IEC, or BS 7671). Always consult a qualified electrician to verify calculations, select appropriate wires, and perform the final installation.