Short answer
Temperature describes a system’s thermal state; heat is energy transferred because of a temperature difference. A thermometer reports temperature. Heat describes energy moving between a system and its surroundings, measured in energy units such as joules. 1 2
A hot object has internal energy, but in careful thermodynamic language it does not “contain heat.” Heat names a transfer, while temperature and internal energy describe aspects of the system’s state. Heating can raise temperature, but it can also melt or boil a substance without increasing its temperature during the phase change. 2 3
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At a glance
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| Question | Heat | Temperature |
|---|---|---|
| What does it describe? | Energy transferred because of a temperature difference. | A property of the thermal state. |
| Typical units | Joules; other energy units are also used. | Kelvin, degrees Celsius, or degrees Fahrenheit. |
| Can a thermometer read it directly? | No; determining transferred energy needs more information. | A suitable thermometer can measure temperature. |
| Does the amount of material matter? | The energy needed for a particular change usually depends on it. | Two different-sized samples can have the same temperature. |
| Is it stored in an object? | Heat is the transfer; internal energy belongs to the object. | Temperature is a state property. |
| Must added heat raise temperature? | No, as a phase change shows. | Temperature may stay steady while energy enters. |
Sources: temperature and equilibrium 1; heat and heat capacity 2; phase changes 3.
What each thing is
Temperature
Temperature is the quantity measured by a thermometer. Two systems in thermal equilibrium have the same temperature: if they can exchange energy thermally, there is no net heat transfer between them. This makes temperature more precise than the everyday sensation of feeling hot or cold. 1
Heat
Heat is a mode of energy transfer driven by a temperature difference. When a warm object and a cooler object interact thermally, energy transfers spontaneously from the warmer to the cooler one. Heat is one way to change internal energy; doing work on a system is another. 2
Key differences
Temperature is not an inventory of energy. Knowing a sample’s temperature does not tell you its mass, material, or total internal energy. A small and a large quantity of the same material can share a temperature while requiring different amounts of energy for an equal temperature change. 2
Heating depends on the material as well as the amount. Under suitable conditions, with no phase change and with other energy transfers accounted for, the familiar approximation is Q = mcΔT. Here Q is transferred heat, m is mass, c is specific heat capacity, and ΔT is temperature change. Different materials have different heat capacities. 2
A temperature rise does not prove that heat entered. Mechanical work can raise internal energy too. Joule’s experiments used mechanical motion to stir water and increase its temperature, helping establish the relationship between work and energy. 2
How to tell them apart
Ask whether the statement concerns a state or an energy transfer. “The water is at 70°F” gives a temperature. “Energy transferred from the warmer water to the cooler surroundings” describes heat transfer.
To calculate a quantity of heat from a temperature change, you need the material, mass, applicable heat capacity, and an account of other energy transfers. A single thermometer reading cannot supply those missing facts. A contact thermometer also needs appropriate thermal contact and time to approach equilibrium with the material it is measuring. 1 2
Where they overlap
Temperature differences drive heat transfer, and that transfer often changes temperature. This close relationship explains why everyday speech blends the words. But the connection is conditional: the same amount of transferred energy can produce different temperature changes in different masses or materials. 2
Edge cases
Melting can absorb energy without warming the sample. During the idealized melting of pure ice at ordinary atmospheric pressure, an ice-water mixture remains near 0°C (32°F) while supplied energy changes ice into liquid. Constant temperature does not mean zero heat transfer. 3
A system need not have one uniform temperature. A material with warmer and cooler regions is not in internal thermal equilibrium. One reading may describe only the location measured, rather than the whole object. 1
Heat capacity is not always constant. It can vary with temperature, and for gases the heating conditions matter. Q = mcΔT is a useful model with assumptions, not a universal shortcut. 2
Why the distinction exists
Thermodynamics needs to track both a system’s state and how energy crosses its boundary. Temperature helps establish equilibrium and the direction of spontaneous thermal transfer. Heat and work describe different ways energy can be transferred. Keeping those ideas separate makes energy accounting possible. 1 2
Common misconceptions
- “Temperature measures stored heat.” It is a state property, not a total-energy reading. 2
- “More heat always means a higher temperature.” A phase change can absorb energy at steady temperature. 3
- “The same temperature means the same energy.” Material and quantity matter. 2
- “Every temperature increase comes from heat transfer.” Work can also increase internal energy. 2
Examples
If two samples of the same liquid start at the same temperature, warming twice the mass through the same temperature change requires about twice the heat, assuming the same heat capacity and no phase change or other energy transfers. Melting an ice-water mixture provides the complementary example: energy can enter while temperature remains nearly steady. These are applications of the models, not claims about an uncontrolled kitchen experiment. 2 3
Sources
Sources checked October 3, 2026.
- OpenStax, University Physics Volume 2 — Temperature and Thermal Equilibrium. Operational temperature and equilibrium.
- OpenStax, University Physics Volume 2 — Heat Transfer, Specific Heat, and Calorimetry. Heat, internal energy, work, and Q = mcΔT.
- OpenStax, University Physics Volume 2 — Phase Changes. Latent heat and changes at constant temperature.