Free Online Calculators
Find the right breaker & cable cross-section
This circuit breaker calculator helps you find the correct breaker rating and cable cross-section for any electrical circuit in seconds. It uses the formula I = P / (U × cos φ) alongside standard wiring regulations to match load to protection. No more guesswork — just enter your power, voltage, and power factor.
Add up the connected load in watts, divide by the circuit voltage to get the current in amps, then add a margin for continuous loads and pick the next standard breaker size at or above that figure. The breaker must also never exceed the ampacity of the wire it protects.
Not immediately — a breaker is built to carry its rated current, so a load right at the rating can run for a long time before the thermal element reacts. Because heat builds up over hours, continuous loads should stay below the rating, which is why circuits are not designed to sit exactly at their limit.
A branch breaker can be rated up to the bus rating of the panel itself, since the main breaker still limits the total current. In practice the size is capped by the physical breaker types the panel accepts and by the load calculation for the remaining circuits.
As many as the total current draw allows — add the amps of every appliance on the circuit and keep the sum comfortably under the breaker rating. Large fixed appliances such as ranges, ovens or dryers normally get their own dedicated circuit instead of sharing one.
Eight-gauge copper with high-temperature insulation is commonly used for that circuit, provided the terminations are rated for the same temperature and the run is not derated for heat or bundling. Aluminium of the same size is not sufficient and needs to be stepped up.
There is no fixed limit on the number of breakers, because the sum of breaker ratings may exceed the panel rating — the real limits are the available spaces and the calculated load of the whole service. If the load calculation shows the service would be overloaded, you need a larger service rather than more breakers.
Yes, if space can be freed up: options are tandem breakers on circuits the panel label allows, combining or removing unused circuits, feeding a subpanel from the existing panel, or replacing the panel with one that has more spaces. The load calculation still has to confirm the service can carry the extra circuit.
As a grounding electrode conductor, six-gauge copper is only accepted where the sole electrode is a driven rod, pipe or plate; connections to concrete-encased or metal water pipe electrodes need a larger conductor. Equipment grounding conductors are sized separately from the breaker rating, so check the table that applies to your case.
Usually yes — range circuits are allowed to be protected above the appliance rating, and the manufacturer's installation instructions state the acceptable breaker size. The wiring must be rated for the breaker, so the conductors have to match the larger figure.
Whether you're planning a new home build, renovating an existing property, or simply adding a new circuit for an appliance, choosing the right circuit breaker size and cable cross-section is essential for electrical safety. Our free Circuit Breaker Calculator makes this process simple, fast, and accurate – no electrical engineering degree required.
An undersized circuit breaker will trip repeatedly under normal load, causing frustration and interrupting power. An oversized breaker, however, won't protect the cable adequately – this can lead to overheating, insulation damage, or even electrical fires. Getting the sizing right is not just about convenience; it's a fundamental electrical safety requirement under standards like IEC 60364 and NEC (National Electrical Code).
Our circuit breaker calculator helps homeowners, electricians, and construction professionals quickly determine the optimal breaker rating and wire gauge before starting any electrical project.
The calculator uses Ohm's Law and standard electrical engineering formulas to determine the correct specifications. Simply enter the following details:
Based on these inputs, the calculator instantly outputs the recommended breaker amperage, the minimum cable cross-section, and flags whether your voltage drop stays within the safe 3% limit.
A standard electric range draws about 7,200 watts at 240V (two-phase in North America, three-phase in Europe). The calculator determines a current of approximately 30A in North America, recommending a 30A double-pole breaker with 10 AWG (or 6 mm²) copper wire. In Europe on a 400V three-phase system, a B16 breaker with 2.5 mm² cable is typically sufficient.
A 3,500W split-system air conditioner running on 230V draws around 15.2A. The calculator recommends a 16A circuit breaker with a minimum of 2.5 mm² copper cable. For cable runs exceeding 20 meters, it advises upgrading to 4 mm² to keep the voltage drop within acceptable limits.
An outdoor socket rated for up to 3,680W (16A at 230V) requires a 16A breaker and at least 1.5 mm² cable for short runs. The calculator will automatically alert you if the cable length causes the voltage drop to exceed 3%, protecting your equipment and ensuring energy efficiency.
Voltage drop refers to the reduction in electrical voltage as current travels along a cable. Most electrical codes limit this to 3% maximum for branch circuits in residential installations. Excessive voltage drop causes poor appliance performance, overheating, and increased energy waste.
Cable cross-sectional area directly affects current-carrying capacity. A 1.5 mm² copper cable can safely carry up to 15.5A when run in a wall, while a 2.5 mm² cable handles up to 21A. The calculator automatically references these capacity tables and recommends a compliant cable size every time.
Not all circuit breakers are the same. The trip curve defines how quickly a breaker responds to overcurrent:
The calculator recommends the appropriate trip curve based on the load type you specify, ensuring your installation is both safe and functional.
This tool is designed for DIY homeowners, licensed electricians, construction project managers, architects, and engineering students. While it provides accurate guidance based on standard formulas, it is intended as a planning aid. All electrical installations should be completed and inspected by a qualified electrician in accordance with local codes.
For a 20-amp outlet, you need a 20A circuit breaker with at least 12 AWG (2.5 mm²) copper wire. The calculator will confirm this and check that the cable length doesn't cause excessive voltage drop.
Yes! The circuit breaker calculator fully supports both single-phase and three-phase electrical systems. Simply select your voltage configuration and enter the total load power.
Using undersized wire creates excessive resistance, which causes heat buildup. In severe cases, this can melt insulation and start a fire. Always use the minimum cable size recommended by the calculator or go one size larger for safety.
No. This calculator is a planning and educational tool. A licensed electrician must design, install, and sign off on all electrical work in compliance with local electrical codes and safety standards.
Absolutely. Our circuit breaker calculator is completely free to use, with no registration or subscription required. Use it as many times as you need for any project.