Convert Pounds per Horsepower-hour to Kilojoules per Kilogram
Pound per Horsepower-hour (lb/(hp·h)) to Kilojoule per Kilogram (kJ/kg) mass-basis fuel efficiency conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 lb/(hp·h) = 5918.3525 kJ/kg
1 Pound per Horsepower-hour = 5918.3525 Kilojoules per Kilogram
1 Kilojoule per Kilogram = 5918.3525 Pounds per Horsepower-hour
1 lb/(hp·h) in every supported unit
Conversion chart: Pound per Horsepower-hour to Kilojoules per Kilogram
Conversion table
| Pound per Horsepower-hour (lb/(hp·h)) | Kilojoule per Kilogram (kJ/kg) |
|---|---|
| 0.01 lb/(hp·h) | 591835.25 kJ/kg |
| 0.1 lb/(hp·h) | 59183.525 kJ/kg |
| 1 lb/(hp·h) | 5918.3525 kJ/kg |
| 2 lb/(hp·h) | 2959.1763 kJ/kg |
| 3 lb/(hp·h) | 1972.7842 kJ/kg |
| 5 lb/(hp·h) | 1183.6705 kJ/kg |
| 10 lb/(hp·h) | 591.83525 kJ/kg |
| 20 lb/(hp·h) | 295.91763 kJ/kg |
| 50 lb/(hp·h) | 118.36705 kJ/kg |
| 100 lb/(hp·h) | 59.183525 kJ/kg |
| 1000 lb/(hp·h) | 5.9183525 kJ/kg |
Pound per Horsepower-hour (lb/(hp·h))
Definition: A classic specific fuel consumption (SFC) rating for reciprocating and turbine engines — pounds of fuel burned per horsepower of output sustained for one hour.
History: Standardized in the early-to-mid 20th century aviation and marine engine industries, when engine output was rated in horsepower and fuel was measured by weight for aircraft loading calculations.
Current use: Still used in piston aero-engine and some marine engine specifications, particularly in the US and in historical/vintage engine documentation.
Kilojoule per Kilogram (kJ/kg)
Definition: A more practically sized specific-energy unit — one thousand joules of energy per kilogram of fuel or material.
History: A natural SI multiple of joule per kilogram, used once raw joule figures for real fuels proved inconveniently large for everyday engineering tables.
Current use: Common in thermodynamics textbooks and engineering reference tables for the calorific value of fuels, refrigerants, and industrial process materials.
Supported Units
| Unit | Symbol | Category |
|---|---|---|
| Joule per Kilogram | J/kg | Specific energy (energy/mass) |
| Kilojoule per Kilogram | kJ/kg | Specific energy (energy/mass) |
| Calorie (IT) per Gram | cal/g | Specific energy (energy/mass) |
| Btu (IT) per Pound | Btu/lb | Specific energy (energy/mass) |
| Kilogram per Kilojoule | kg/kJ | Specific fuel consumption (mass/energy) |
| Gram per Calorie (IT) | g/cal | Specific fuel consumption (mass/energy) |
| Pound per Btu (IT) | lb/Btu | Specific fuel consumption (mass/energy) |
| Pound per Horsepower-hour | lb/(hp·h) | Specific fuel consumption (mass/energy) |
| Gram per Kilowatt-hour | g/kWh | Specific fuel consumption (mass/energy) |
About These Parameters
- Value
- The fuel-efficiency figure you want to convert, expressed in the "From" unit. Accepts decimals.
- From Unit
- The unit your input value is currently measured in — a specific-energy unit like J/kg or Btu/lb, or an engine SFC unit like g/kWh.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly.
How Fuel Efficiency - Mass Conversion Works
The Formula
Within the same group (both specific energy, or both specific fuel consumption), conversion is a simple multiplication:
result = value × (factor of "From" unit ÷ factor of "To" unit)
Crossing between the two groups instead inverts through the base unit:
SFC unit = (factor of SFC unit) ÷ (value × factor of specific-energy unit)
For Pound per Horsepower-hour → Kilojoule per Kilogram: 1 lb/(hp·h) = 5918.3525 kJ/kg.
Specific Energy vs. Specific Fuel Consumption
Specific energy (J/kg, cal/g, Btu/lb) describes a fuel's raw calorific value — an intrinsic property of the fuel itself, independent of any engine. Specific fuel consumption (g/kWh, lb/(hp·h)) instead describes how efficiently a real engine turns that stored energy into usable mechanical output, and depends on the engine's thermal efficiency, not just the fuel. A lower SFC figure always means a more fuel-efficient engine, the opposite direction from specific energy, where a higher figure means a more energy-dense fuel.
Why g/kWh Replaced lb/(hp·h)
Pounds per horsepower-hour was the standard engine efficiency rating through the early-to-mid 20th century, when horsepower was the universal power unit in aviation and marine engineering. As engine testing and international trade shifted to the metric kilowatt, grams per kilowatt-hour became the global standard — it's the figure printed on virtually every modern diesel and gasoline engine's technical datasheet today.
Example
A diesel engine rated at 200 g/kWh converts to about 0.32879736 lb/(hp·h) — a typical figure for a modern, efficient diesel; older or smaller gasoline engines often run well above 250 g/kWh.
Frequently Asked Questions
How many Kilojoules per Kilogram are in 1 Pound per Horsepower-hour?
1 Pound per Horsepower-hour (lb/(hp·h)) equals exactly 5918.3525 Kilojoules per Kilogram (kJ/kg).
Why does a lower g/kWh mean a better engine, when higher J/kg means a better fuel?
They measure different things in opposite directions. J/kg (specific energy) is a property of the fuel — more energy per kilogram is always better. g/kWh (specific fuel consumption) is a property of the engine — it asks how much fuel mass is spent to deliver one unit of output, so less fuel for the same output means a more efficient engine.
Can I convert a fuel's calorific value directly into an engine's SFC rating?
This converter performs the mathematical reciprocal between the two groups, but that number alone assumes a perfectly (100%) efficient engine. Real engines lose energy to heat, friction, and exhaust, so an actual SFC rating is always numerically worse (higher) than the theoretical reciprocal of the fuel's calorific value.
How accurate are these conversions?
Every conversion factor used here is the exact, internationally recognized relationship between the underlying energy, mass, and power units (e.g. 1 kWh = exactly 3,600,000 joules) — results are limited only by floating-point display precision, not by rounded conversion constants.