KEVOS® MAKEOS · Engineering
Fuel Oil Heating Value from Baumé Gravity (Specific Gravity, Heat per kg and per Litre, Fuel Use)
What is the approximate heating value of a fuel oil from its Baumé gravity or specific gravity, per kilogram and per litre, and how much oil will a burner or heater use to deliver my heat output?
Fuel oil heating value by the handbook’s approximate formula BTU per pound = 18,650 + 40 × (degrees Baumé − 10), with the Baumé scale for liquids lighter than water, specific gravity = 140 ÷ (130 + degrees Baumé), so that either can be entered; the value in MJ/kg, MJ/L and BTU per US gallon, and the oil burned per hour and over a running time to deliver a heat output at the appliance efficiency you enter.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Gravity given as | choice | Enter the oil’s gravity on the Baumé hydrometer scale or as a specific gravity. |
| Degrees Baumé | °Bé | Degrees on the Baumé hydrometer scale for liquids lighter than water, from the oil supplier or a hydrometer reading. |
| Specific gravity | Specific gravity of the oil relative to water, both at 60 °F (15.6 °C). | |
| Heat demand | ||
| Heat output needed | kW | Useful heat the burner, boiler or heater must deliver. |
| Appliance efficiency (from its data) | % | Efficiency of the appliance from its data plate or test, the share of the fuel’s heat that becomes useful heat. |
| Running time | h | Hours the appliance runs at that output, for the fuel used over the period. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Gravity given as
- What it is
- Whether the oil gravity is entered in degrees Baumé or as a specific gravity.
- Units and format
- Choose one of 2 options from the list: Degrees Baumé (liquid lighter than water); Specific gravity (60/60 °F).
- Example
- The form opens with “Degrees Baumé (liquid lighter than water)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Chooses which of the two gravity inputs is used.
- Get it right
- Supplier sheets may give API gravity instead; convert that first.
What this means: Degrees Baumé
- What it is
- Gravity of the oil on the Baumé hydrometer scale for liquids lighter than water.
- Units and format
- Enter a number in °Bé: °Bé. The form accepts 10 °Bé to 100 °Bé. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 26.9 °Bé as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher Baumé means a lighter oil with more heat per kilogram.
- Get it right
- Read the hydrometer at 60 °F (15.6 °C) or correct the reading to it.
What this means: Specific gravity
- What it is
- Specific gravity of the oil relative to water, both at 60 °F.
- Units and format
- Enter a plain number with no unit. The form accepts 0.6 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.89 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lighter oil gives a higher heating value per kilogram.
- Get it right
- Fuel oils are about 0.82 to 0.95; take it from the supplier’s certificate.
Heat demand
What this means: Heat output needed
- What it is
- Useful heat the burner, boiler or heater must deliver.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0 kW to 1000000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Oil burned rises in proportion.
- Get it right
- Use the heat load, not the burner’s maximum firing rate.
What this means: Appliance efficiency (from its data)
- What it is
- Efficiency of the appliance: the share of the fuel’s heat that becomes useful heat.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0.000001% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Lower efficiency burns more oil for the same output.
- Get it right
- Take it from the data plate or a combustion test; check whether it is on gross or net heating value.
What this means: Running time
- What it is
- Hours the appliance runs at the heat output entered.
- Units and format
- Enter a number in h: hours. The form accepts 0 h to 100000 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only changes the oil used over the period.
- Get it right
- Use equivalent full-load hours for a varying load.
Method and formulas
- Specific gravity = 140 ÷ (130 + degrees Baumé) for liquids lighter than water; degrees Baumé = 140 ÷ specific gravity − 130.
- Heating value ≈ 18,650 + 40 × (degrees Baumé − 10) BTU/lb; 1 BTU/lb = 2.326 kJ/kg.
- Density = specific gravity × 999.0 kg/m³ (water at 60 °F); heat per litre and per US gallon follow.
- Oil burned = heat output ÷ (efficiency × heating value).
- Example: oil of 26.9 °Bé has a specific gravity of 0.89229 and about 19,326 BTU/lb (44.952 MJ/kg); 100 kW at 80 % needs about 11.23 L/h.
Limitations
- The heating value formula is an approximate fit to samples of petroleum oils from heavy crude to gasoline (about 18,500 to 21,100 BTU/lb); use the supplier’s tested value when there is one.
- The formula gives the gross (higher) heating value; appliance efficiencies quoted on the net value need the lower figure.
- For liquids heavier than water the Baumé scale uses specific gravity = 145 ÷ (145 − degrees Baumé); fuel oils are lighter than water.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Estimate the heating value of an oil from its gravity
- Estimate burner fuel use for a heat demand
- Convert between Baumé degrees and specific gravity
Who it is for
- Boiler and furnace operators
- Plant engineers
- Estimators
What you get
- Degrees Baumé and specific gravity
- Heating value in BTU/lb, MJ/kg and MJ/L
- Heating value per US gallon
- Oil burned per hour (kg/h and L/h)
- Oil used over the running time
Interpreting the result
- Lighter oils (higher Baumé) carry more heat per kilogram but less per litre.
- Fuel use scales directly with heat output and inversely with efficiency.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 381, 2694, 3012. Topic reference; no source tables or recommended settings are reproduced.
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