Foot Pound to Joule Converter
Convert foot pound joule between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Foot Pound to Joule Converter
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Formula: J = ft-lbf x 1.35582 | 1 BTU = 1055.06 J | 1 cal = 4.184 J
Worked example — 350 ft-lbf = 474.54 J = 474.54 Nm
Formula
J = ft-lbf x 1.35582 | 1 BTU = 1055.06 J | 1 cal = 4.184 J
One foot-pound equals 1.35582 joules. The joule is the SI unit of energy defined as the work done by a one-newton force through one meter. Key relationships: 1 BTU = 1,055.06 J, 1 calorie = 4.184 J, 1 kWh = 3,600,000 J. The foot-pound measures work in Imperial units (one pound of force through one foot).
Worked Examples
Example 1: Engine Torque Conversion
Problem:An engine produces 350 ft-lbf of torque. Convert to joules and newton-meters.
Solution:Joules: 350 x 1.35582 = 474.537 J Newton-meters: 474.537 Nm (same as joules for energy) Kilojoules: 474.537 / 1000 = 0.4745 kJ BTU: 474.537 / 1055.06 = 0.4498 BTU
Result:350 ft-lbf = 474.54 J = 474.54 Nm
Example 2: Energy Comparison
Problem:Convert 5,000 joules to foot-pounds, calories, and BTU.
Solution:Foot-pounds: 5,000 / 1.35582 = 3,688.10 ft-lbf Calories: 5,000 / 4.184 = 1,195.22 cal Kilocalories: 5,000 / 4,184 = 1.195 kcal BTU: 5,000 / 1,055.06 = 4.739 BTU
Result:5,000 J = 3,688.1 ft-lbf = 1,195.2 cal = 4.74 BTU
Frequently Asked Questions
How do I convert foot-pounds to joules?
To convert foot-pounds to joules, multiply by 1.35582. One foot-pound (ft-lbf) is the energy needed to exert a force of one pound through a distance of one foot. For example, 100 foot-pounds equals 135.582 joules. The foot-pound is commonly used in US engineering for torque specifications on engines and fasteners, while the joule is the SI standard energy unit used internationally.
What is the difference between a foot-pound of energy and a foot-pound of torque?
A foot-pound of energy (ft-lbf) and a foot-pound of torque (lb-ft) have the same dimensions but different physical meanings. Energy foot-pounds measure work done when a force moves through a distance. Torque foot-pounds (often written lb-ft in automotive contexts) measure rotational force around an axis. Numerically they are equivalent, but conventionally energy uses ft-lbf while torque uses lb-ft to distinguish the concepts.
How many joules are in a BTU?
One British thermal unit (BTU) equals approximately 1,055.06 joules or about 778.17 foot-pounds. The BTU is defined as the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. BTUs are widely used in the US for rating heating and cooling equipment, natural gas pricing, and energy efficiency of appliances. In metric countries, the equivalent calculations use kilojoules or kilocalories instead.
What is an erg and how does it relate to a joule?
An erg is the CGS (centimeter-gram-second) unit of energy equal to exactly 0.0000001 joules (10^-7 J). One joule equals 10 million ergs. The erg is defined as the work done by a force of one dyne acting through one centimeter. While largely replaced by the joule in modern science, ergs still appear in astrophysics literature where extremely large energies are expressed in ergs. A supernova releases about 10^44 joules or 10^51 ergs of energy.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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