A buyer compares two air compressors: Model A lists 3.5 horsepower, Model B lists 2,600 watts. Marketing copy calls both “heavy duty.” Electricians think in amps, facilities think in kilowatts, and procurement sees horsepower from the legacy PDF. Without converting power to one unit, you rank narratives instead of capability.
This guide walks a product-spec scenario: normalize power before comparing efficiency, duty cycle, or electrical load. Verify with a Power Converter.
The scenario: competing spec sheets
Power measures energy per time (watts = joules per second). Mechanical horsepower and metric horsepower differ slightly from kilowatts. Marketing rounds aggressively. Scenario-first comparison picks a canonical unit (often kilowatts for facility load, watts for electronics) and converts every candidate.
Useful anchors
- 1 mechanical horsepower ≈ 745.7 watts ≈ 0.7457 kW.
- 1 kilowatt = 1000 watts.
- A 15-amp US household circuit at 120 V is not 15 kW—volts and amps matter; do not confuse power with current.
If a space heater claims 1500 W, that is 1.5 kW—compare fairly to a 2 kW industrial heater, not to a 2 HP motor without conversion.
Electrical power vs mechanical power
Motor nameplates may list output horsepower and input electrical watts separately. Efficiency lives in the gap. Converting only the headline HP number without input watts understates operating cost.
Worked example: compressor comparison
Model A: 3.5 HP → about 3.5 × 745.7 ≈ 2610 W. Model B: 2600 W. After conversion, nameplate power is similar, but duty cycle, tank size, and flow (CFM) still decide fitness. Power conversion narrows the field; it does not replace engineering requirements.
BTU per hour and heating labels
HVAC sometimes lists BTU/h. 1 watt ≈ 3.412 BTU/h. When comparing a gas furnace rating to an electric heater in watts, convert both to the same unit before judging capacity for a room—then still check climate sizing methods.
Duty cycle and peak vs continuous
Power specs may cite peak surge (microwave inverter) vs continuous draw. Compare like with like. A device that peaks at 2000 W but averages 900 W belongs on different rows in a load table.
Practical workflow for buyers
- Collect nameplate photos and PDF spec tables.
- Convert all power figures to kW in a spreadsheet column.
- Note input vs output power where motors are involved.
- Add duty cycle and efficiency footnotes.
- Size electrical supply from input watts and power factor if provided.
Sanity checks
After converting, ask whether the device could plausibly run on the circuit described. A 5 kW appliance on a 15 A / 120 V circuit is impossible without tripping—catch spec typos early.
EV charging and battery labels
Chargers list kW delivery; battery capacity is often kWh (energy, not power). Convert marketing “7 kW home charger” separately from “60 kWh pack.” Duration math needs energy and power distinct: hours to fill ≈ kWh / kW only when efficiency and taper curves are understood—power conversion is step one, not the whole model.
Solar inverters and nameplate AC output
PV modules list DC watts; inverters list AC output in kW. Compare converted DC nameplate sums to AC inverter limits to see clipping risk. Again, conversion aligns units; it does not replace irradiance modeling.
Facility load planning
Sum input watts for simultaneous equipment, apply diversity factors per electrical code or facilities standards, and compare to service capacity. A column of converted kW values makes load meetings faster than rereading PDF footnotes.
Audio and amplifier “watts”
Audio marketing uses watts for output power; definitions vary (RMS vs peak). Convert numbers for rough comparisons only after reading whether the spec is continuous or peak—physics alignment still needs the footnote.
Data center rack budgets
IT equipment lists nameplate watts; facilities plan cooling in kW. Convert each line, sum, and leave headroom. Nameplate is often higher than measured draw—note when you use measured vs rated in the same table.
Generator and UPS sizing conversations
Backup power meetings mix kW (real power) and kVA (apparent power). Converting watts to kilowatts is only step one; power factor and surge lists still belong to the electrician. Bring converted kW tables so mechanical and electrical stakeholders start from aligned numbers.
Industrial motors on sale sheets
Clearance listings sometimes drop the unit entirely and show a bare number for motor size—confirm HP vs kW with the nameplate photo before purchase. Converted kilowatts belong in the comparison table next to duty cycle and frame size.
Heat pumps and COP
Coefficient of performance links heat output to electrical input. Marketing may highlight heat kW while the panel lists input kW—convert and label each column before comparing models for a retrofit quote.
Motor efficiency classes
IE3 and IE4 labels describe efficiency tiers, not power units. After converting horsepower to kilowatts, compare efficiency tables from the same standard rather than mixing regions.
Industrial motors on sale sheets
Clearance listings sometimes drop the unit entirely and show a bare number for motor size—confirm HP vs kW with the nameplate photo before purchase. Converted kilowatts belong in the comparison table next to duty cycle and frame size.
Heat pumps and COP
Coefficient of performance links heat output to electrical input. Marketing may highlight heat kW while the panel lists input kW—convert and label each column before comparing models for a retrofit quote.
Motor efficiency classes
IE3 and IE4 labels describe efficiency tiers, not power units. After converting horsepower to kilowatts, compare efficiency tables from the same standard rather than mixing regions.
Try it before the next capital request
Attach a conversion column to procurement templates. Use the Power Converter so HP, kW, and W sort on physics, not typography. Decisions get faster because numbers speak the same language.