Circuit Breaker & Fuse Calculator

This breaker fuse size calculator turns raw load and conductor inputs into the protective-device ratings that belong in a clean product record. Paste a load in amps or watts, pick a voltage and phase, and get a recommended circuit breaker and fuse size along with the standard rating you should publish on the listing.

What it checks

• Full-load current derived from your power input (watts or kVA), system voltage, and single- or three-phase configuration, so the same SKU resolves to one consistent amperage value.
• Recommended breaker rating rounded up to the next standard frame size from the common series (15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100 A and beyond).
• Recommended fuse rating with the equivalent standard ampere step, flagged separately from the breaker because the two ladders are not identical.
• Continuous-load adjustment that applies the conventional 125 percent sizing margin for loads expected to run three hours or more.
• Mismatch flags when a value already in your catalog (a stated breaker amperage, a fuse class, or a listed amp draw) is inconsistent with what the inputs imply.

How the breaker fuse size calculator works

The calculator applies the standard relationships used across electrical product data. Single-phase current is power divided by voltage; three-phase current divides by voltage times the square root of three. Continuous loads are scaled by 125 percent before the result is rounded up to the nearest standard ampere rating, because protective devices are manufactured in fixed steps rather than continuous values. Breaker and fuse ladders are evaluated independently since a 35 A calculated load may land on a 40 A breaker but a different standard fuse step.

Every calculation runs entirely in your browser. Nothing you paste is uploaded, stored, or sent to a server, so it is safe to run against a confidential supplier price file or an unreleased catalog. That matters for the enrichment use case: distributors often need to backfill protection ratings across thousands of MRO and industrial SKUs where the manufacturer datasheet states a load but never the recommended device size. The same pattern shows up beyond electrical goods. A furniture distributor normalizing power specs on motorized desks, a CPG operation tagging the breaker requirement on commercial refrigeration units, or an industrial reseller cleaning up motor and pump listings all face the identical problem: a stated load with no derived, standardized protection value.

Treat the output as a normalized, source-traceable attribute. When you push a calculated breaker or fuse rating into a PIM, record how it was derived so a reviewer can later see the load and voltage it came from rather than an unexplained number. That provenance is what separates trustworthy enrichment from a guess, and it is the same discipline a canonical product record depends on across every attribute.

Related resources

FAQ

How do I calculate the right breaker size for a load? +

Find the full-load current first: divide power by voltage for single-phase, or by voltage times the square root of three for three-phase. If the load runs continuously for three hours or more, multiply by 125 percent. Then round up to the next standard breaker rating. The calculator above does each step and returns the standard size.

What is the difference between breaker sizing and fuse sizing? +

Both protect against overcurrent, but they are manufactured in different standard steps and respond differently to overloads. A calculated current can land on one standard breaker rating and a different standard fuse rating, so the tool evaluates the two ladders separately rather than assuming they match.

Why apply a 125 percent factor? +

For loads expected to operate at full draw for three hours or more, the conventional rule sizes the protective device at 125 percent of the continuous current. This headroom prevents nuisance tripping and accounts for sustained heating. For short-duty loads the factor does not apply.

Is my data uploaded anywhere? +

No. All calculation happens in your browser. Nothing you paste leaves your device, so you can safely run the tool against confidential price files, supplier exports, or unreleased catalog data.

Can I use this to enrich a whole product catalog? +

Use it to confirm the logic and spot-check values. For thousands of SKUs you want the same calculation applied automatically, validated against existing data, and written back with provenance. That is the catalog-scale version of this tool, and it is what Claro automates for distributor enrichment.