Flash Point Estimator
Estimate the flash point of a hydrocarbon from its boiling point, with GHS hazard classification and a reference table of measured values for common liquids.
The flash point is the lowest temperature at which a liquid produces enough vapor to briefly ignite when an ignition source is present. It is one of the most important safety parameters for handling flammable liquids.
Measuring flash point requires specialized equipment (Pensky-Martens closed cup or Tag closed cup). When no measured value is available, a rough estimate can be made from the normal boiling point using a simple linear relationship:
Tf = 0.683 * Tb + 15 (both temperatures in Kelvin)
Read the limits before you use the number. This relationship is fitted to hydrocarbons, and only there does it behave. For alkanes and aromatics it lands within a few degrees: heptane predicts −4 C against a measured −4, toluene 4 C against 4, decane 47 C against 46.
For anything with oxygen or nitrogen in it the estimate falls apart, and it fails in the dangerous direction. Ethanol predicts about −18 C against a measured +13 C. Methanol predicts −27 C against +11 C. Acetone predicts −33 C against −20 C. A liquid that the correlation calls far more volatile than it is will be over-classified rather than under-classified, but the error is large enough that the number is simply not usable. Look these up instead of estimating them.
Measured flash points for common liquids (closed cup):
| Liquid | Flash point |
|---|---|
| Diethyl ether | −45 C |
| Acetone | −20 C |
| Benzene | −11 C |
| Heptane | −4 C |
| Toluene | 4 C |
| Methanol | 11 C |
| Ethanol | 13 C |
| Isopropanol | 12 C |
| Xylene | 27 C |
| Kerosene | 38 to 72 C |
| Diesel | 52 to 96 C |
| Motor oil | ~230 C |
| Vegetable oil | 250 to 330 C |
Flammability classification (GHS / OSHA HCS):
- Category 1: flash point below 23 C and boiling point at or below 35 C (e.g. diethyl ether)
- Category 2: flash point below 23 C and boiling point above 35 C (e.g. acetone, ethanol, toluene)
- Category 3: flash point 23 C up to 60 C (e.g. xylene, kerosene, most diesel)
- Category 4: flash point above 60 C up to 93 C (combustible liquids)
- Not classified as a flammable liquid: flash point above 93 C
Note that a liquid above 60 C is not “non-flammable”. Diesel and many solvent blends sit in Category 4 and will burn readily once heated or absorbed into a wick such as rag or lagging.
Never rely on an estimated flash point for a safety decision. Use the measured value from the safety data sheet before handling any material.
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This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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