Live table for your input

After you convert, this table shows your value in multiple common units at once. It’s intentionally formatted to be screenshot-friendly for sharing (or for a quick sanity check when you’re bouncing between electrical specs, engine specs, and HVAC specs).

Note: dBm is a logarithmic unit. When converting to dBm from watts, the formula uses dBm = 10·log10(P[mW]). When converting from dBm to watts, it uses P[W] = 10^((dBm−30)/10).

Share-ready snapshot text

People share converters when the output is instantly understandable. The Copy Snapshot button generates a neat text block with your conversion + a few popular equivalents. Paste it into Slack, Discord, WhatsApp, or a comment thread.

• 750 W ≈ 0.75 kW ≈ 1.01 hp ≈ 2559 BTU/hr
• “That’s basically a hair dryer / microwave power range.”

Power conversion formulas (with plain-English meaning)

Power is one of those concepts that shows up everywhere: electricity bills, engine specs, heat pumps, data centers, audio gear, and even radio transmitters. The tricky part is that different industries keep different “favorite” units. Electrical and physics contexts usually use watts (W). Engines often use horsepower (hp). HVAC loves BTU/hr and tons of refrigeration. Telecom and IT often use dBm because it compresses huge ranges into manageable numbers.

The good news: almost all conversions become simple once you pick a single “base” unit. This calculator uses watts as the base. In other words, it converts your input to watts first, then converts watts into your target unit. That approach is reliable, avoids round-trip drift, and keeps the code simple.

Metric prefixes are just powers of 10:

• 1 kW = 1000 W
• 1 MW = 1,000,000 W
• 1 GW = 1,000,000,000 W

If you ever forget: k = thousand, M = million, G = billion. Converting between these is just moving the decimal point. Example: 2.5 kW = 2500 W, and 2500 W = 0.0025 MW.

“Horsepower” sounds singular, but it isn’t. Several definitions exist historically. The most common in the U.S. for engines is mechanical horsepower:

• 1 mechanical hp ≈ 745.699872 W (often rounded to 746 W)

Some specs use metric horsepower (often called PS or cv depending on country), which is based on 75 kilogram-force meters per second:

• 1 metric hp ≈ 735.49875 W
• 1 PS = 735.49875 W (commonly treated the same as metric hp)

If you’re converting an engine spec for a quick comparison, mechanical vs metric hp usually differs by about 1–2%. That’s small, but it can matter when you’re comparing products or doing a cost estimate.

BTU stands for British Thermal Unit — a unit of energy. When you see BTU/hr, you’re looking at energy per hour, which is power. The standard conversion used here is:

• 1 W ≈ 3.412141633 BTU/hr
• 1 BTU/hr ≈ 0.29307107 W

“Tons of refrigeration” comes from the cooling power needed to freeze one short ton of water into ice over 24 hours. In modern HVAC work it’s effectively fixed at:

• 1 ton (refrigeration) = 12,000 BTU/hr ≈ 3516.852842 W

That means a 2-ton AC system is roughly 24,000 BTU/hr of cooling capacity. Converting to watts can help compare against electrical input power, though remember: cooling capacity is not the same as electrical consumption.

dBm is common in RF and networking because it compresses massive ranges. The “m” means it’s referenced to 1 milliwatt. The formulas:

• dBm = 10 · log10(P[mW])
• P[W] = 10^((dBm − 30) / 10)

Why the “−30”? Because 1 W = 1000 mW, and 10·log10(1000) = 30. So, 0 dBm = 1 mW, 30 dBm = 1 W, and 40 dBm = 10 W. That mental map alone helps a lot when you’re checking a radio transmitter, amplifier, or Wi‑Fi spec.

Bottom line: this converter doesn’t “guess.” It uses known constants and careful base-unit math to keep results consistent.

What the calculator does step-by-step

The converter uses a simple two-step pipeline:

Each unit has a factor that tells us how many watts it represents. For example, if you choose “kW” as the input unit, the factor is 1000. If you type 2.5 kW, the converter computes: watts = 2.5 × 1000 = 2500 W. For most units, this is a straight multiplication or division.

Once the value is in watts, the converter divides by the target unit’s “watts per unit” factor. Example: to convert 2500 W to mechanical horsepower: hp = 2500 ÷ 745.699872 ≈ 3.35 hp.

dBm is logarithmic, so it can’t be handled with a single constant factor like W or kW. Instead:

• If your input is dBm, the converter calculates watts using 10^((dBm−30)/10).
• If your output is dBm, the converter calculates dBm using 10·log10(P[mW]).

Converters get annoying when they either over-round (losing meaning) or under-round (spamming decimals). “Auto (smart)” rounds based on the magnitude: large numbers get fewer decimals, small numbers keep more decimals so they don’t turn into “0.00”. If you want strict control, choose 2, 4, or 6 decimals.

Differences usually come from one of these:

• Horsepower definition: mechanical hp vs metric hp vs PS.
• BTU constants: some references use slightly different rounding.
• Displayed precision: the internal math may match, but the rounded display can differ.

If you’re comparing two sources, match the unit definition and increase the displayed decimals. That usually resolves “mystery” differences instantly.

Common conversions people look up

Many household space heaters are rated around 1500 W. Converting to kilowatts: 1500 W ÷ 1000 = 1.5 kW. If electricity costs $0.15/kWh and you run a 1.5 kW heater for 2 hours, you’ll use about 3 kWh (≈ $0.45).

A “2 hp” motor (mechanical horsepower) converts to: 2 × 745.699872 ≈ 1491.4 W. That’s “power output” in the horsepower sense; the electrical input may be higher due to efficiency losses.

12,000 BTU/hr is 1 ton of refrigeration. In watts: 12,000 × 0.29307107 ≈ 3516.9 W, which is 3.5169 kW. Again: that’s cooling capacity, not necessarily electrical draw.

30 dBm equals 1 watt. Using the inverse formula: P[W] = 10^((30−30)/10) = 10^0 = 1 W. 20 dBm = 0.1 W, and 40 dBm = 10 W — each +10 dB is a 10× power change.

1 kW = 1000 W. Multiply by 3.412141633 to get BTU/hr: 1000 W ≈ 3412 BTU/hr. That’s where the popular “kW to BTU” mental shortcut comes from.

Frequently Asked Questions

• Is horsepower the same everywhere?

  Not exactly. “hp” can mean mechanical horsepower (~745.7 W) or metric horsepower (~735.5 W). This converter includes both, plus PS. If you’re converting an engine spec, use the definition that matches the region or datasheet.

• Why does my AC say “2 tons” but it doesn’t weigh 2 tons?

  “Tons” here means tons of refrigeration, a cooling capacity unit: 1 ton = 12,000 BTU/hr. It’s an old historical definition based on freezing water into ice over time, not the equipment’s weight.

• Does watts to BTU/hr convert electricity to heat?

  It converts power units. If an electric heater is nearly 100% efficient at turning electricity into heat, then 1 W of electrical input becomes about 3.412 BTU/hr of heat output. But for devices like AC systems, the relationship is not direct because you’re moving heat, not generating it.

• What is dBm and why do networking people love it?

  dBm is a logarithmic power unit relative to 1 milliwatt. It makes it easier to compare signal levels across large ranges, and it plays nicely with decibels (dB) gains/losses from amplifiers and cables.

• Can I use this converter offline?

  Yes — once the page is loaded, the math runs fully in your browser. There’s no login and no server-side conversion call.

• How accurate is the converter?

  It uses standard constants and double-precision math. Any “difference” you see is usually rounding or a different horsepower/BTU convention elsewhere. Choose more decimals for tighter comparisons.

More tools you might like

Jump to related calculators and popular pages: