Horsepower to Joules Calculator
Convert power (Horsepower) to energy (Joules) with time duration
- What is Horsepower?
- What is a Joule?
- Real-World Examples
- How to Convert Horsepower to Joules
- The Conversion Process
- Horsepower to Joules Formula
- Mechanical Horsepower (Most Common)
- Metric Horsepower (PS)
- Electrical Horsepower
- Examples of HP to Joules Conversion
- Example 1: Small Engine Running for 1 Minute
- Example 2: Car Engine for 1 Hour
- Example 3: Electric Motor for 30 Seconds
- Conversion Tables
- Horsepower to Joules (1 Second Duration)
- Common Time Durations (10 HP Example)
- Common FAQs
- Related Power & Energy Calculators
- Author
What is Horsepower?
Horsepower (HP) is a unit of power—the rate at which work is done or energy is transferred. Originally defined by James Watt in the 18th century to compare steam engine output to the power of draft horses, it remains widely used today, especially in automotive and mechanical engineering.
There are three main types of horsepower:
- Mechanical Horsepower (hp) = 745.7 watts — Used in USA, UK (most common)
- Metric Horsepower (PS) = 735.5 watts — Used in Europe, “Pferdestärke”
- Electrical Horsepower = 746 watts — Exactly defined for electrical motors
Horsepower measures power (energy per time), not energy itself. To find energy in joules, you must multiply horsepower by time: Energy = Power × Time.
Understanding horsepower is essential when working with engines, motors, and mechanical systems. For related power calculations, see our Horsepower to Watts Calculator.
What is a Joule?
A joule (J) is the SI unit of energy—the capacity to do work. Named after physicist James Prescott Joule, it represents the energy transferred when one watt of power is applied for one second.
One joule equals:
- 1 watt × 1 second (W·s)
- 1 newton × 1 meter (N·m) of force applied over distance
- The energy needed to lift 100 grams by 1 meter against Earth’s gravity
- 0.239 calories (small calorie)
Real-World Examples
- A 100-watt light bulb uses 100 joules per second
- A car traveling at 60 mph has about 470,000 joules of kinetic energy
- A typical AA battery stores about 9,360 joules
- One food calorie (kcal) equals 4,184 joules
For energy conversions, explore our Joules to Kilowatts Calculator.
How to Convert Horsepower to Joules
Converting horsepower to joules requires understanding that horsepower is power (energy per time) while joules measure energy. You must multiply power by time to get energy.
The Conversion Process
Step 1: Convert horsepower to watts
Step 2: Convert time to seconds
Step 3: Multiply watts by seconds to get joules
1 Watt = 1 Joule per second. So if you have power in watts and time in seconds, simply multiply them together to get energy in joules.
Horsepower to Joules Formula
The formula depends on which type of horsepower you’re using:
Mechanical Horsepower (Most Common)
HP = Mechanical Horsepower
t = Time in seconds
745.7 = Conversion factor (watts per HP)
Metric Horsepower (PS)
735.5 = Conversion factor (watts per PS)
Electrical Horsepower
For power-only conversions without time, use our Horsepower to Kilowatt Converter.
Examples of HP to Joules Conversion
Example 1: Small Engine Running for 1 Minute
Problem: A 5 HP lawn mower engine runs for 1 minute. How much energy is produced?
Given:
• Power = 5 HP (mechanical)
• Time = 1 minute = 60 seconds
Formula: E = HP × 745.7 × t
Calculation:
E = 5 × 745.7 × 60
E = 223,710 Joules (223.71 kJ)
Real-world context: This is enough energy to lift a 2,000 kg car about 11.4 meters high.
Example 2: Car Engine for 1 Hour
Problem: A 150 HP car engine operates for 1 hour. Calculate the total energy output.
Given:
• Power = 150 HP
• Time = 1 hour = 3,600 seconds
Calculation:
E = 150 × 745.7 × 3,600
E = 402,678,000 Joules
E = 402.68 MJ = 111.9 kWh
Real-world context: This is roughly equivalent to the energy in 3 gallons of gasoline.
Example 3: Electric Motor for 30 Seconds
Problem: A 1 HP electric motor runs for 30 seconds. Find the energy consumed.
Given:
• Power = 1 HP (electrical) = 746 W
• Time = 30 seconds
Calculation:
E = 1 × 746 × 30
E = 22,380 Joules (22.38 kJ)
For more motor calculations, see our Horsepower to Amps Calculator.
Conversion Tables
Horsepower to Joules (1 Second Duration)
Common Time Durations (10 HP Example)
Common FAQs
No. Horsepower is power (energy per time), while joules measure energy. You must multiply horsepower by time to get energy. Without a time duration, you can only convert HP to watts (both are power units).
Mechanical horsepower (745.7 W) is used in the USA and UK, while metric horsepower or PS (735.5 W) is used in Europe. The difference is about 1.4%, so for most calculations they’re interchangeable, but use the correct one for precision.
A 1 HP motor running for 1 hour uses 2,684,520 joules (2.68 MJ or 0.746 kWh). This assumes mechanical horsepower at 100% efficiency.
Horsepower remains popular in automotive and mechanical industries due to tradition and consumer familiarity. Many people intuitively understand “300 HP” better than “224 kW,” even though watts are the SI standard. For power conversions, see our Watts to Horsepower Calculator.
Multiply horsepower-hours by 2,684,520 to get joules. For example, 1 HP-hr = 2,684,520 J = 2.68 MJ. This is equivalent to 0.746 kWh. For reverse calculations, use our Joule to Horsepower-Hour Calculator.
Almost, but not exactly. Electrical horsepower is defined as exactly 746 watts, while mechanical horsepower is 745.7 watts. The difference is negligible (0.04%) for most applications.
