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Breaker Sizing Calculator

By Muhammad Abdullah Rauf · Founder, EverydayTools.proUpdated 2026-03-01

What size breaker do I need?

Breaker sizing starts with **load amps = Watts ÷ Volts**. For **continuous loads**, multiply by **1.25**, then pick the **next standard breaker** that meets or exceeds that value.

**Standard sizes:** 15, 20, 25, 30, 35, 40, 50, 60 A (and higher)

**Example — 5,500 W electric dryer at 240 V:**

5,500 ÷ 240 = **22.9 A**

22.9 × 1.25 = **28.6 A design**

Next standard breaker: **30 A**

Minimum wire: **10 AWG** copper (30 A ampacity)

Breaker rating must not exceed wire ampacity. This calculator pairs recommended wire with breaker size.

Standard breaker selection

Converts watts to amps, applies continuous factor, selects next standard breaker and matching minimum copper wire.

Formula

Design amps = (Watts ÷ Volts) × 1.25 if continuous → next standard breaker ≥ design amps

Assumptions

  • Single-phase resistive load.
  • Standard US breaker sizes.
  • Copper NM-B 60°C wire pairing.

Limitations

  • Does not replace permit, inspection, or local code amendments.
  • Motor circuits need separate starting-current analysis.

How to use Breaker Sizing Calculator

  1. Enter appliance watts

    Use nameplate watts for the largest load on the new circuit.

  2. Enter circuit voltage

    120 V for general branch; 240 V for dryer, range, and water heater.

  3. Set continuous load

    Enable for dryers, ranges, and equipment that runs 3+ hours at full load.

  4. Read breaker and wire

    Result shows standard breaker size and minimum matching copper wire gauge.

Breaker Sizing Calculator examples

Dryer circuit

Input

5,500 W · 240 V · continuous

Output

30 A breaker

Window AC

Input

1,200 W · 120 V

Output

15 A breaker

Who uses Breaker Sizing Calculator?

Common real-world scenarios where this tool saves time.

Electric dryer

5,500 W at 240 V continuous → 30 A breaker, 10 AWG.

Window AC

1,200 W at 120 V non-continuous → 15 A breaker, 14 AWG.

Electric range

8,000 W at 240 V → 40 A breaker, 8 AWG.

Workflow guides

Step-by-step chains that connect related tools for common tasks.

New appliance circuit

  1. Size breaker here
  2. Confirm wire in Wire Gauge Calculator
  3. Check circuit load if sharing a panel slot

Reference tables

Standard residential breaker sizes

BreakerTypical useMin copper wire
15 AGeneral 120 V outlets14 AWG
20 AKitchen, bath, workshop12 AWG
30 ADryer, small water heater10 AWG
40 ARange, large appliances8 AWG

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Frequently Asked Questions

What breaker for a 240V dryer?

Most residential dryers need a 30 A double-pole breaker on 10 AWG copper — confirm nameplate amps on your model.

Can breaker be larger than wire allows?

No — breaker must protect wire ampacity. This calculator shows minimum wire for the recommended breaker.

15 or 20 amp outlets?

General 120 V branch circuits use 15 A (14 AWG) or 20 A (12 AWG) breakers — match wire gauge to breaker.

What breaker for a 5,500 W dryer?

At 240 V continuous load, 5,500 W draws ~22.9 A — use a 30 A breaker with 10 AWG copper minimum.

Does a 20 A breaker need 12 AWG wire?

Yes — 20 A breakers require at least 12 AWG copper NM-B; 14 AWG is only rated for 15 A circuits.

Privacy, accuracy, and trust

Privacy

Appliance watts and voltage are processed only in your browser — EverydayTools does not store circuit inputs.

Estimate only — not NEC certification or permit approval. Licensed electricians required for new circuits.

Part of Calculator Tools

More free tools for the same workflow.

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Reviewed on 2026-03-01.