⚡ Calculated Amperage
Power Breakdown
Full Calculation Table
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How to Use the Amperage Calculator
Pick Find Amps if you know the equipment's wattage and want the current draw. Pick Find Watts if you know the amperage from a clamp meter or breaker rating and want the equivalent power.
Most residential and small commercial equipment in Canada runs single phase. Larger commercial compressors, chillers, and rooftop units usually run three phase.
Pick the nameplate voltage from the list, or enter a custom value. Then enter the watts or amps depending on which mode you selected.
Resistive loads like heat strips use 1.0. Motors and compressors run lower, typically 0.85 to 0.95. Use the nameplate power factor if it's printed.
Click Calculate to see the result along with apparent power in kVA and real power in kW.
Converting Between Amps and Watts for HVAC Equipment
Amperage tells you how much current a piece of equipment draws, and it's the number that determines wire size, breaker size, and disconnect rating. Wattage tells you how much power the equipment uses. The two are connected by voltage and power factor, and this calculator moves between them in either direction.
Single-Phase vs. Three-Phase Formulas
For a single-phase load, amps equal watts divided by voltage times power factor. For a three-phase load, you also divide by the square root of 3, which is about 1.732. This extra factor exists because three-phase power splits the load across three conductors instead of two, so each conductor carries less current for the same total power. A 15 kW three-phase heater draws noticeably less current per leg than the same 15 kW load running single phase.
Why Power Factor Matters
Power factor measures how efficiently current converts into usable work. Pure resistive loads, like electric heat strips, have a power factor of 1.0, meaning all the current does useful work. Motors and compressors have inductive windings that pull extra current without doing extra work, dropping the power factor to somewhere between 0.8 and 0.95 depending on the motor design and load. Ignoring power factor on a motor calculation will underestimate the actual amp draw, sometimes by 10% to 20%. Our power factor calculator works out a precise value from real and apparent power if you have both numbers from a meter reading.
Reading a Nameplate
Most HVAC equipment nameplates list RLA (Rated Load Amps) or FLA (Full Load Amps) directly, which is more accurate than calculating from wattage since it accounts for the equipment's actual measured power factor and efficiency. Use this calculator when you only have a wattage rating, like on a baseboard heater or electric furnace element, or when you need to convert a known amp draw into an equivalent wattage for load calculations.
Next Steps After Finding Amperage
Once you have the amp draw, use the wire size calculator to pick the right conductor gauge, and the breaker size calculator to confirm overcurrent protection. For equipment with a compressor or large motor, check the single phase calculator or three phase calculator for a more detailed circuit-level breakdown including starting current.
A Note on Accuracy
This calculator gives a close estimate using standard formulas and typical power factor ranges. For permit-stamped electrical work, always use the manufacturer's nameplate FLA or MCA value when one is available, since it reflects the actual tested performance of that specific unit rather than a generic formula.
Frequently Asked Questions
For single-phase loads, divide watts by the product of voltage and power factor: amps equals watts over (volts times power factor). For three-phase loads, also divide by the square root of 3: amps equals watts over (volts times 1.732 times power factor). Most resistive heat strips use a power factor near 1.0, while motors and compressors typically run between 0.8 and 0.9. The power factor calculator helps you pin down an exact value.
If the nameplate doesn't list a power factor, 0.85 is a reasonable estimate for most single-phase compressors and condenser fan motors. Three-phase compressors often run slightly higher, around 0.88 to 0.92. For permit-accurate work, use the nameplate-listed amperage directly instead of calculating from wattage when one is available. See the three phase calculator for a closer look at three-phase compressor circuits.
Three-phase power delivers the same total wattage across three conductors instead of two, so the current carried by each conductor is lower by a factor of the square root of 3, or about 1.732. This is one reason larger HVAC equipment, like commercial rooftop units and chillers, runs three phase: it moves more power through smaller, less expensive conductors.
Use the nameplate FLA or MCA value whenever it's available, since it reflects the equipment's actual tested performance. This calculator is best for situations where you only have a wattage rating, like a resistive heat strip or baseboard heater, or when you're estimating amp draw for equipment that hasn't been selected yet. For wire and breaker sizing on permit work, the MCA / MOCP calculator uses the proper code-required method.
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