EleCalculator

Safety & Protection calculator

Circuit Breaker Sizing Calculator

This page starts with the standard-size answer most users need: 10, 15, 20, 25, 30, 35, 40, 45, 50, and 60A are the common low-voltage NEC breaker sizes before you move into larger feeder ratings. It then screens continuous, non-continuous, mixed, and motor loads while keeping 12 AWG and 10 AWG small-conductor limits separate from the motor inverse-time path.

Updated June 21, 2026

Common NEC standard breaker sizes are 10, 15, 20, 25, 30, 35, 40, 45, 50, and 60A. A 16A continuous load screens to a 20A review point, and 12 AWG copper still stays capped at 20A on a general branch circuit.

16A continuous x 125% = 20A | 12 AWG copper -> 20A max under NEC 240.4(D)

Enter load current, load type, and selected conductor below to screen the next standard breaker review point and catch wire-limit conflicts early

Calculator Inputs

Quick Presets

Full-load current or calculated branch-circuit load in amperes

Select the load category that drives the NEC sizing path

Used for the conductor compatibility review after derating

For project context only; breaker sizing is based on amperes

Simplified 75°C correction factor for the conductor check

Simplified adjustment factor for more than three current-carrying conductors

Calculation Results

Enter values above to see calculation results

Field kit

Tools for breaker checks

Use the breaker result as a review point, then compare non-invasive tools for tracing, measuring, and documenting circuits.

Compare clamp metersFor load current checksOpens in a new tabFind breaker findersFor circuit tracingOpens in a new tabAdd panel labelsFor documentationOpens in a new tab

As an Amazon Associate I earn from qualifying purchases.

Opens in a new tabOpens in a new tabOpens in a new tab
Calculation history

Example Calculations

16A Continuous Branch Circuit

A continuous 16A load is sized at 125% before picking a standard breaker.

Inputs
  • Load Current: 16 A
  • Load Type: Continuous
  • Selected Conductor: 12 AWG Copper

34A Motor Full-Load Current

A motor circuit follows the simplified inverse-time breaker path and a separate conductor ampacity review.

Inputs
  • Load Current: 34 A FLC
  • Load Type: Motor
  • Selected Conductor: 8 AWG Copper

How to Use

How This Breaker Size Calculator Works

This page is designed for the questions electricians and maintenance teams ask most often: What are the standard breaker sizes? What breaker review point should I start with for a continuous load? Can 12 AWG go on a 25A breaker? The short answer is that common low-voltage sizes start at 10A, 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, and 60A, a 16A continuous load lands on 20A, and 12 AWG copper still stays capped at 20A on a general branch circuit. The calculator then walks through the same logic in a transparent, simplified NEC-style workflow.

Inputs used by the calculator

  • Load current is the circuit load or motor full-load current in amperes.
  • Load type selects the sizing path: non-continuous, continuous, mixed, or motor.
  • Selected copper conductor is used for the conductor compatibility review after derating.
  • Ambient temperature factor and current-carrying conductor factor reduce the simplified conductor ampacity check when the installation runs hotter than the base condition.

General-purpose load path

  1. Non-continuous loads are sized at 100% of load current.
  2. Continuous loads are sized at 125% of load current.
  3. The result is rounded up to the next standard breaker size for review.
  4. The selected conductor is checked against a simplified ampacity review plus the small-conductor breaker limits used on common branch circuits.

Motor load path

Motor branch circuits are not checked the same way as ordinary branch circuits. This calculator uses a simplified inverse-time breaker path for motors and then performs a separate conductor ampacity review. That keeps the breaker screening from incorrectly treating the motor breaker rating as if it had to match the general-purpose conductor limit one-for-one.

Common NEC standard breaker sizes

Common standard sizes Typical use
10A, 15A, 20A, 25A, 30A Small branch circuits, controls, receptacle and appliance circuits
35A, 40A, 45A, 50A, 60A Larger branch circuits and small feeders
70A through 225A Feeders, panelboards, and larger equipment circuits
250A and above Larger feeders, services, and industrial distribution

For a field-reference version of the same standard-size sequence, open the Breaker Size Chart. After the breaker screen, continue to the Wire Size Calculator and Ampacity Calculator before treating the result as ready for installation.

Small-conductor breaker limits used in this calculator

Copper conductor General branch-circuit breaker limit Common use
14 AWG 15A Lighting and general 15A branch circuits
12 AWG 20A 20A kitchen, bathroom, garage, and general-use circuits
10 AWG 30A Dryers, water heaters, and similar 30A circuits

A 12 AWG copper conductor may show more than 20A in a table column, but that does not automatically make it acceptable on a 25A general branch-circuit breaker. That is why this page treats the small-conductor rule as a separate check instead of relying only on ampacity numbers.

What this calculator does not model automatically

  • Detailed motor overload sizing and controller coordination.
  • Field verification of terminal temperature ratings and manufacturer markings.
  • Every exception that can permit or restrict the next-higher standard breaker size in special circuit conditions.
  • Interrupting-rating checks against available fault current, SCCR review, selective coordination, or permit-level engineering approval.

Common Applications

Checking common standard breaker sizes before laying out a new branch circuit

Verifying continuous-load breaker sizing for EV charging, HVAC, and lighting

Reviewing whether a selected copper conductor can support the intended breaker

Screening motor branch circuits before a detailed motor-protection review

Frequently Asked Questions

What are the most common standard breaker sizes?
The most common low-voltage standard breaker sizes are 10A, 15A, 20A, 25A, 30A, 35A, 40A, 45A, 50A, and 60A. Larger feeder and service work commonly steps into 70A, 80A, 90A, 100A, 125A, 150A, 175A, 200A, and beyond.
What breaker do I need for a 16A continuous load?
A 16A continuous load is sized at 125%, so the minimum breaker calculation is 20A. You still have to verify that the selected conductor can legally support that breaker.
Can 12 AWG copper go on a 25A general branch-circuit breaker?
Not in the simplified branch-circuit review used here. Even if a table ampacity looks higher, 12 AWG copper is still treated as a 20A small conductor for common general-purpose breaker selection.
Why can a motor breaker look much larger than the motor conductor ampacity?
Motor branch-circuit short-circuit and ground-fault protection does not work like ordinary branch-circuit overcurrent protection. The breaker can be significantly larger than the conductor ampacity because overload protection is handled separately.

Related Calculators

Browse all calculators

Wire Size Calculator

Handle conductor gauge selection from load current, standard OCPD, and voltage drop after ampacity and raceway constraints are known.

Explore

Ampacity Calculator

Individual conductor ampacity and derating per NEC 310.16 with ambient-temperature correction, current-carrying conductor adjustment, and terminal-rating limits.

Explore

Short Circuit Calculator

Screen available fault current from transformer impedance, feeder impedance, or known source impedance.

Explore

Motor Branch Protection Calculator

Screen NEC Article 430 motor branch-circuit short-circuit and ground-fault protective device sizing.

Explore

Electrical Panel Load Calculator

Evaluate panel loading, demand, and spare capacity against NEC-style design assumptions.

Explore

Arc Flash Calculator

Screen adjusted incident energy and approximate arc flash boundary from a known base case.

Explore