Power Converter: W, kW, hp, PS, BTU/h and dBm

What the power converter does

The power converter changes a value between eight units: watt (W), kilowatt (kW), megawatt (MW), mechanical horsepower (hp), metric horsepower (PS), BTU per hour (BTU/h), foot-pound-force per second (ft·lbf/s) and decibel-milliwatt (dBm). The watt heads the list; the rest are the units engine badges, HVAC labels and radio link budgets still carry.

Every linear entry is an exact ratio to the watt. Mechanical horsepower is 550 ft·lbf/s, or 745.6998715822702 W with the 1959 foot and pound definitions; metric PS is 75 kgf·m/s, exactly 735.49875 W. BTU/h divides the International Table unit (1055.05585262 J) by 3600, which is 0.2930710701722… W, and ft·lbf/s is 1.3558179483314004 W. dBm is deliberately different: a logarithmic level against 1 mW, where 0 dBm = 1 mW and 30 dBm = 1 W.

Energy is a separate conversion: watt-hours, calories and Btu belong to the energy converter.

How to use it

Both cards offer the same eight units; the page opens on W → kW with 1 filled in. Pick your unit on the left, your target on the right.
Type on either card and the other side converts as you type; the swap button exchanges the pair and carries the value across.
Either field accepts expressions: 75+35 shows a quiet = 110 hint and converts the running value, and Enter or = settles it. An expression with no finite value, such as 1/0, keeps the last settled value and shows = ?.
The All Units list repeats the value in all eight units; click a row to move that unit to the focused card. The keypad button opens a standard calculator.

Worked examples

Every readout below comes from this converter.

Set the cards to	Readout
1 kW → mechanical hp	1.3410220896 hp
1 kW → metric PS	1.3596216173 PS
1 hp → W	745.699871582 W
1 PS → W	735.49875 W
1 hp → PS	1.0138696654 PS
1 BTU/h → W	0.2930710702 W
1 ft·lbf/s → W	1.3558179483 W
1 W → dBm	30 dBm

Two bigger jobs from the same table: a 110 kW engine is 147.512429855 hp, or 149.558377903 PS when the badge uses metric horsepower; a 12,000 BTU/h air conditioner is 3,516.85284207 W, the figure cooling calls one ton of refrigeration.

Limits and precision

Display rounding.: Readouts keep 12 significant digits: between 10⁻¹⁰ and 10¹⁵ they print with comma grouping and at most 10 decimal places, and outside that band in exponential form with six decimals (1.000000e+15). The screen is thinner than the stored value: 1 BTU/h is 0.2930710701722… W and reads 0.2930710702 W, while 1 ft·lbf/s in MW reads 0.0000013558 MW. Calculations carry the stored value.
dBm has edges.: Zero or negative power has no dBm level and reads --- dBm; in the other direction, 0 dBm is 0.001 W and 30 dBm is 1 W. Adding dBm values adds ratios, not watts.
What it doesn't do.: It converts power values only: no energy over time (kWh), no torque multiplied by rotational speed, no volts times amps and no power factor, and the list has neither electric horsepower (746 W) nor calories per second. Energy totals go to the energy converter; torque and V × A arithmetic go to the scientific calculator; pressure ratios belong to the pressure converter.

The horsepower trap

One English word, two different numbers, side by side in the same dropdown; the label is the only clue — "Horsepower (mechanical)" for hp, "Horsepower (metric)" for PS:

Mechanical hp is 550 ft·lbf/s, or 745.6998715822702 W; metric PS is 75 kgf·m/s, or 735.49875 W. One hp is 1.0138696654 PS, and one PS is 0.9863200706 hp — metric horsepower is about 1.4% smaller.
The same 110 kW engine is 147.512429855 hp in one entry and 149.558377903 PS in the next, about 2.05 hp apart. When a source says only "hp", convert to W or kW first.
Electric horsepower is a third definition, exactly 746 W, and it is not one of the eight entries; "1 hp = 746 W" fits motor nameplates, not this list.

Where people use it

Engines and motors

A 110 kW drivetrain is 147.512429855 hp for US badges and 149.558377903 PS for European ones; a spare 3 hp pump draws 2.2370996148 kW.

Heating and cooling

North American HVAC quotes BTU/h while European nameplates quote kW: 12,000 BTU/h — the ton of refrigeration — is 3,516.85284207 W, and a single BTU/h is 0.2930710702 W.

Radio and wireless

Link budgets run on dBm: 1 W of transmit power is 30 dBm, and 0 dBm is 0.001 W. Convert back to watts before adding powers; in the level domain, 3 dB roughly doubles the power.

Privacy

All input and calculation run inside your browser and are never uploaded. This page is static text; it neither contains nor records user input.

References

BIPM, The International System of Units (SI Brochure), 9th edition — the watt as the SI unit of power, 1 W = 1 J/s. bipm.org （访问日期：2026-09-30）
NIST Special Publication 811, Appendix B.8 — factors for horsepower (550 ft·lbf/s), horsepower (metric), horsepower (electric), foot pound-force per second, BtuIT per hour and the ton of refrigeration. nist.gov （访问日期：2026-09-30）
Wikipedia, Horsepower — imperial horsepower = 550 ft·lbf/s = 745.69987158227022 W, metric horsepower = 75 kgf·m/s = 735.49875 W, and electric horsepower exactly 746 W. en.wikipedia.org （访问日期：2026-09-30）
Wikipedia, dBm — a power level relative to 1 mW: 0 dBm = 1 mW, 30 dBm = 1 W, and zero power has no finite dBm value. en.wikipedia.org （访问日期：2026-09-30）
Wikipedia, British thermal unit — the International Table Btu built from 4.1868 J/cal and 453.59237 g/lb, and the ton of refrigeration at 12,000 BTU/h. en.wikipedia.org （访问日期：2026-09-30）

Sources & review

Reviewed by: CalcX Editorial Team
Updated: 2026-09-30