Attowatt is 1e-18 watt units.
Attowatts to Horsepowers Converter — aW to hp
Convert Attowatt (aW) to Horsepower (hp) using the exact conversion factor (1 attowatt = 1.341022e-21 horsepower). See the formula, worked examples, conversion table, history, and common uses.
Attowatts to Horsepowers converter
Converter
Power Converter
Convert watts, horsepower, refrigeration tons, BTU per hour, and engineering power units.
Context values
Some unit families need one extra value for a physically accurate result.
Mechanical horsepower.
Result = input x 1e-18 / 745.6998716.
Power uses the watt as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Attowatts to Horsepowers
Attowatt and Horsepower both describe power output, and the conversion is a routine part of comparing an engine or motor's spec sheet across countries that use different power units. Specifically: Attowatt is 1e-18 watt units, and mechanical horsepower.
Formula
horsepowers = attowatts × 1.341022e-21
This factor comes from each unit's defined relationship to the category's base unit: 1 attowatt equals 1e-18 base units, and 1 horsepower equals 745.699871582 base units, so dividing one by the other gives the direct attowatt-to-horsepower factor of 1.341022e-21.
Simple example
1 aW × 1.341022e-21 = 1.341022e-21 hp
1 attowatt = 1.341022e-21 horsepowers.
Real-world example
100 aW × 1.341022e-21 = 1.341022e-19 hp
100 attowatts = 1.341022e-19 horsepowers.
Conversion table
| Attowatt (aW) | Horsepower (hp) |
|---|---|
| 1 aW | 1.341022e-21 hp |
| 10 aW | 1.341022e-20 hp |
| 100 aW | 1.341022e-19 hp |
| 500 aW | 6.70511e-19 hp |
| 1,000 aW | 1.341022e-18 hp |
| 5,000 aW | 6.70511e-18 hp |
Reverse conversion: Horsepower to Attowatt
1.341022e-21 hp × 7.456999e+20 = 0.9999999332 aW
1.341022e-21 horsepowers = 0.9999999332 attowatts.
attowatts = horsepowers × 7.456999e+20
For a page dedicated to this direction, see Horsepower to Attowatt.
Understanding the Attowatt (aW)
Attowatt is 1e-18 watt units.
Understanding the Horsepower
Horsepower (hp) measures power. Mechanical horsepower is defined as exactly 745.6998715822702 watts. It is classified as a US/imperial customary unit.
Where it's used: United States and United Kingdom (vehicle and engine specifications)
Mechanical horsepower vs. metric horsepower. Mechanical horsepower (745.7 W) and metric horsepower/PS (735.5 W) differ by about 1.4% — a US car spec sheet in 'hp' and a European one in 'PS' are not directly comparable numbers without conversion.
Uses of the Horsepower today
- US and UK vehicle engine power ratings
- Motor and engine specifications in English-speaking markets
History of the Horsepower
James Watt popularized horsepower in the 1780s as a marketing figure, comparing his steam engines' output to the working capacity of a horse (based on his estimate of a horse turning a mill), so buyers could grasp engine capability in familiar terms. The unit stuck long after its origin as a sales tool, eventually being formally defined at exactly 550 foot-pounds per second.
Historical origin. Horsepower was not the invention of a single named person; it developed through the process described above.
Horsepower — sources
- NIST Special Publication 811 — Documents the exact watt-equivalence of mechanical horsepower.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many horsepowers are in 1 attowatt?
1 attowatt equals 1.341022e-21 horsepowers, using the exact defined conversion factor rather than an estimate.
How do I convert attowatt to horsepower?
Multiply the attowatt value by 1.341022e-21. The converter above does this instantly to whatever precision you set.
How do I convert horsepower back to attowatt?
Use the reverse factor: 1 horsepower equals 7.456999e+20 attowatts. You can also use the swap control in the converter above to flip the direction instantly.
What is a attowatt?
Attowatt (aW) is a unit of power.
What is a horsepower?
Horsepower (hp) measures power. Mechanical horsepower is defined as exactly 745.6998715822702 watts. It is classified as a US/imperial customary unit.
Is the attowatt to horsepower conversion exact?
Yes. Mechanical horsepower is defined as exactly 745.6998715822702 watts. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between mechanical horsepower vs. metric horsepower?
Mechanical horsepower (745.7 W) and metric horsepower/PS (735.5 W) differ by about 1.4% — a US car spec sheet in 'hp' and a European one in 'PS' are not directly comparable numbers without conversion.