Convert thermal units across heat density, heat flux density, heat transfer coefficient, specific heat capacity, thermal conductivity, thermal expansion.
Last updated
Thermal units
Choose the thermal quantity first
Convert heat density, heat flux density, heat transfer coefficient, specific heat capacity, thermal conductivity, thermal expansion coefficient, and thermal resistance units from one notation to another. The panels stay separated because these quantities answer different engineering questions.
No false direct conversions Use this as a thermal units converter, not a heat-transfer solver. Heat per area, heat flux, coefficient, specific heat capacity, conductivity, expansion coefficient, and R-value are not interchangeable without the missing physical inputs.
Active quantity
Thermal conductivity
Convert material conductivity such as W/(m*K), BTU/(ft*h*deg F), and cal/(cm*s*deg C).
Use this panel for material or fluid conductivity. R-value, U-factor, and heat-loss rate need geometry, thickness, and boundary inputs before they can be related.
Result
0.6 W/(m·K)
Base SI thermal conductivity for the stated material-property value.
SI and calorie-based units
Watts per metre-kelvin0.6 W/(m·K)
Watts per centimetre-kelvin0.006 W/(cm·K)
Kilowatts per metre-kelvin6e-4 kW/(m·K)
Calories per cm-second-°C0.0014 cal/(cm·s·°C)
Kilocalories per m-hour-°C0.5159 kcal/(m·h·°C)
BTU-based units
BTU per foot-hour-degree Fahrenheit0.3467 BTU/(ft·h·°F)
BTU per inch-hour-degree Fahrenheit4.1601 BTU/(in·h·°F)
Common thermal reference checks
These anchors help spot a wrong family selection before copying a value into a spreadsheet, material note, insulation comparison, or heat-transfer worksheet.
Family
Reference check
Equivalent
Use
Heat density
1 langley
41,840 J/m²
Solar and radiant-exposure notes where the source is accumulated heat per area.
Heat flux density
1 BTU/(h·ft²)
3.15459 W/m²
Wall, surface, or radiation-rate checks when the source still includes time.
Heat transfer coefficient
1 BTU/(h·ft²·°F)
5.67826 W/(m²·K)
U-factor, film-coefficient, and convection references that are already per temperature difference.
Specific heat capacity
Water reference
4,184 J/(kg·K)
Quick sanity check for cal/(g·°C), BTU/(lb·°F), and material heat-capacity tables.
Thermal conductivity
Still-air reference
0.026 W/(m·K)
Material-property comparison before relating conductivity to thickness, R-value, or U-factor.
Thermal expansion
12 ppm/°C
12 µm/(m·°C)
Engineering CTE notation where ppm, microstrain, and micrometre-per-metre values are aliases.
Thermal resistance
RSI 2.5
R-14.1957 and U 0.4 W/(m²·K)
Building-envelope checks where SI RSI and US R-value need to stay area-normalised.
Thermal quantity comparison
Quantity
Answers
Typical units
Do not mix with
Heat density
How much heat or radiant exposure is accumulated per area
J/m^2, kWh/m^2, langley, BTU/ft^2
Do not compare directly with W/m^2 unless a time basis is supplied.
Heat flux density
How fast heat crosses or leaves each unit of area
W/m^2, kW/m^2, BTU/(h*ft^2)
Do not treat it as total heat, conductivity, or a coefficient.
Heat transfer coefficient
Heat flux per temperature difference for a film, surface, or assembly
W/(m^2*K), BTU/(h*ft^2*deg F)
Do not reuse the value without the original boundary condition or assembly definition.
Specific heat capacity
Heat needed per mass per temperature interval
J/(kg*K), cal/(g*deg C), BTU/(lb*deg F)
Do not use it for total heat unless mass and temperature change are known.
Thermal conductivity
A material property for heat conduction through thickness
W/(m*K), BTU/(ft*h*deg F)
Do not confuse it with R-value or U-factor without geometry and thickness.
Thermal expansion
Strain per temperature interval for a material
1/K, ppm/K, um/(m*deg C), uin/(in*deg F)
Do not calculate actual movement without length and temperature change.
Thermal resistance
Area-normalised resistance to heat flow
m^2*K/W, ft^2*h*deg F/BTU
Do not mix it with electronics-style total deg C/W unless area has been normalised.
Thermal units converter: heat density, heat flux, conductivity, specific heat, expansion
A thermal units converter is useful only when it keeps the thermal quantity visible. This page also explains the main assumptions behind the thermal units converter result, highlights the supporting figures shown by the calculator, and helps the reader use the estimate without overstating what a quick online tool can prove.
Why thermal units must be separated by quantity family
Thermal references often place energy, heat rate, material properties, insulation values, and temperature-interval notation close together. A direct unit conversion should stay inside one physical quantity. A value in kWh/m2 is accumulated heat per area; a value in W/m2 is a heat-transfer rate per area; a value in W/(m*K) is a material conductivity; and an R-value is an area-normalised thermal resistance.
The calculator therefore starts with a quantity-family choice. It converts heat density, heat flux density, heat transfer coefficient, specific heat capacity, thermal conductivity, thermal expansion coefficient, and thermal resistance in separate panels. It does not infer duration, area, mass, temperature difference, thickness, starting length, material range, or whole-assembly details unless those inputs belong to the same unit family.
Heat density conversions: J/m2, kWh/m2, langley, and BTU/ft2
Heat density in this suite means accumulated heat per unit area. It is useful for radiant exposure, seasonal energy per surface area, solar summaries, and legacy heat-load notes where the value is a total amount over an event or reporting period.
Use the heat density panel for J/m2, kJ/m2, MJ/m2, Wh/m2, kWh/m2, cal(th)/cm2, langley, BTU (IT)/ft2, and BTU (th)/ft2. Do not use it for W/m2 or BTU/(h*ft2), because those units still include a time-rate basis.
1 kWh/m2 = 3.6 MJ/m2
A kilowatt-hour is a fixed energy amount, so the area-normalised form converts directly.
1 langley = 1 cal(th)/cm2 = 41840 J/m2
Langley and thermochemical calorie per square centimetre are equivalent radiant-exposure forms.
Heat flux density and heat transfer coefficient conversions
Heat flux density describes heat-transfer rate divided by area. It answers how quickly heat is crossing or leaving a surface per unit area, so units such as W/m2, kW/m2, W/cm2, BTU/(h*ft2), kcal/(h*m2), and cal/(s*cm2) belong in one panel.
A heat transfer coefficient adds the driving temperature difference to that rate-per-area idea. It is used for local film coefficients, convection estimates, boiling and condensation work, and overall U-style summaries. Convert it inside the coefficient panel using units such as W/(m2*K), kW/(m2*K), kcal/(h*m2*deg C), cal/(s*cm2*deg C), and BTU/(h*ft2*deg F).
q'' = Qdot / A
Heat flux density is heat-transfer rate per area.
q'' = h * DeltaT
A heat transfer coefficient links heat flux density to a temperature difference in a coefficient model.
Specific heat capacity and thermal conductivity conversions
Specific heat capacity is a material property that states how much heat is needed per unit mass per temperature interval. The panel keeps SI, thermochemical calorie, International Table calorie, and BTU interval forms visible because Celsius, kelvin, Fahrenheit, and Rankine interval notation can otherwise be copied into spreadsheets incorrectly.
Thermal conductivity is a different material property. It describes heat conduction through a material per thickness and temperature gradient. It can be converted between W/(m*K), W/(cm*K), kW/(m*K), cal/(cm*s*deg C), kcal/(m*h*deg C), BTU/(ft*h*deg F), and BTU/(in*h*deg F), but it cannot become an R-value or U-factor without geometry and thickness.
1 cal(th)/(g*deg C) = 4184 J/(kg*K)
Common thermochemical calorie relationship used in specific heat capacity references.
1 BTU/(lb*deg F) = 4186.8 J/(kg*K)
International Table BTU relationship used for common imperial heat-capacity notation.
Thermal expansion and thermal resistance conversions
Coefficient of thermal expansion describes strain per temperature interval. The panel keeps reciprocal-temperature notation, engineering notation, ppm, and microstrain aliases together. Celsius and kelvin interval forms stay numerically aligned, while Fahrenheit and Rankine forms need interval conversion.
Thermal resistance in this converter means area-normalised insulation or envelope resistance, commonly written as RSI in SI work or R-value in US customary work. The panel also shows reciprocal U-value context, but it does not turn a product label into a complete wall, roof, floor, or window result.
1 ppm/K = 1 microstrain/K = 1 um/(m*K) = 1e-6 /K
Small-strain coefficient aliases used in thermal expansion tables.
1 m2*K/W = about 5.678 ft2*h*deg F/BTU
Direct conversion between RSI and the common US insulation R-value form.
U = 1 / R
Reciprocal thermal transmittance for an area-normalised resistance in the same unit system.
Reference checks for common thermal unit mistakes
The calculator now keeps a compact reference-check table near the active panel because thermal unit mistakes often happen when a familiar constant is copied into the wrong family. One langley should land at 41,840 J/m2 in heat density, while 1 BTU/(h*ft2) belongs in heat flux and lands at about 3.15459 W/m2. A similar-looking coefficient, 1 BTU/(h*ft2*deg F), belongs in the heat transfer coefficient family and lands at about 5.67826 W/(m2*K).
Material-property checks stay separate as well: water's specific heat capacity is about 4,184 J/(kg*K), still air's conductivity reference is near 0.026 W/(m*K), and 12 ppm/deg C is the same small-strain coefficient as 12 um/(m*deg C). In the resistance panel, RSI 2.5 converts to about R-14.1957 and reciprocal U 0.4 W/(m2*K), which is useful only when the value is area-normalised.
1 BTU/(h*ft2) = about 3.15459 W/m2
Heat flux density keeps the time-rate basis but does not include a temperature difference.
1 BTU/(h*ft2*deg F) = about 5.67826 W/(m2*K)
Heat transfer coefficient and U-factor-style units include the temperature-difference basis.
RSI 2.5 = about R-14.1957 and U 0.4 W/(m2*K)
Thermal resistance can be converted and inverted only after confirming it is area-normalised.
What this consolidation keeps and what stays separate
The old specialist pages overlapped because they all handled thermal unit translation. Combining them into one thermal units converter makes the physical boundaries clearer while keeping each long-tail query represented in panel names, examples, formulas, FAQ coverage, and result labels.
Energy, power, and fuel energy density remain separate pages. They answer broader questions that are not limited to thermal-property conversion, so they should not be folded into this suite unless a future pass adds a fully integrated and clearly separated workflow.
Frequently asked questions
Can I convert heat density directly to heat flux density?
Not with a pure unit converter. Heat density is accumulated heat per area, while heat flux density is heat-transfer rate per area. You need the duration or time model before moving from one to the other.
Is heat flux density the same as thermal conductivity?
No. Heat flux density is a result per area, such as W/m2. Thermal conductivity is a material property, such as W/(m*K). Relating them requires a conduction model, geometry, thickness, and temperature gradient.
Is a heat transfer coefficient the same as a U-factor?
Sometimes the units look similar, but the context matters. A local film coefficient and an overall U-factor are both coefficient-style quantities, yet they should not be mixed unless the source definition and boundary conditions match.
How do I convert J/(kg*K) to cal/(g*deg C) for specific heat capacity?
Use the specific heat capacity panel. A value in J/(kg*K) is divided by 4184 to get thermochemical cal/(g*deg C). The panel also keeps International Table calorie and BTU interval conventions visible.
Can thermal conductivity convert to R-value?
Not directly. Conductivity needs a material thickness before it can become an area-normalised resistance. This converter keeps conductivity and thermal resistance in separate panels to avoid that dimensional mistake.
Why is ppm per degree C included with thermal expansion?
Many material tables express coefficient of thermal expansion as ppm/deg C, microstrain/deg C, or um/(m*deg C). Those are equivalent small-strain notations for the same coefficient when the temperature interval is the same.
How do I convert RSI to a US R-value?
Use the thermal resistance panel. Multiply RSI in m2*K/W by about 5.678 to get the common US R-value in ft2*h*deg F/BTU. The panel also shows reciprocal U-value context.
Should I use this page for electronics thermal resistance in deg C/W?
Usually no. Electronics thermal resistance in deg C/W is often a total component or junction-to-case value, not an area-normalised insulation value. This page keeps to area-normalised R-value and RSI units.
Why did Calcipedia combine these thermal converters?
The previous pages served closely related unit-reference tasks. Combining them into one thermal units converter preserves the specialist keyword coverage while reducing thin overlap and making the physical boundaries clearer on one page.
Are energy converter, power converter, and fuel energy density converter part of this page?
No. Those pages remain separate because they cover broader energy and power workflows. This page focuses on thermal unit families where the risk is confusing related heat-transfer and material-property quantities.
