An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range that varies depending on device function and application context, and ranges from minimum operating temperature to maximum operating temperature (or peak operating temperature ). The device may fail outside this range of safe operating temperatures .
It is a component of reliability engineering .
Similarly, biological systems have a feasible temperature range, which may be called the “operating temperature”.
Most equipment is manufactured in several temperature grades. The widely accepted grades  are:
- Commercial: 0° to 70°C
- Industrial: -40° to 85°C
- Force: -55° to 125°C
Nevertheless, each manufacturer defines its own temperature grade, so designers should pay close attention to the actual datasheet specifications. For example, Maxim Integrated uses five temperature grades for its products: 
- Full Military: −55 °C to 125 °C
- Automotive: -40°C to 125°C
- AEC-Q100 Level 2: −40 °C to 105 °C
- Extended Industrial: -40°C to 85°C
- Industrial: -20°C to 85°C
The use of such grades ensures that an appliance is suitable for its application, and will withstand the environmental conditions in which it is used. Normal operating temperature ranges are affected by many factors, such as the power dissipation of the device.  These factors are used to define a device’s “threshold temperature”, i.e. its maximum normal operating temperature, and the maximum operating temperature after which the device will no longer function. Between these two temperatures, the device will operate at a non-peak level.  For example, a resistor may have a threshold temperature of 70 °C and a maximum temperature of 155 °C, between which it exhibits a thermal derivative . 
For electrical devices, the operating temperature can be the junction temperature ( Tj ) of the semiconductor in the device. The junction temperature is affected by the ambient temperature, and for integrated circuits , the equation is given by:
wherein Tj is the junction temperature in °C, Ta is the ambient temperature in °C, Pd is the power dissipation of the IC in W , and Rja is the thermal resistance of the junction to ambient in °C/W.
Aerospace and military
Electrical and mechanical equipment used in military and aerospace applications may need to tolerate greater environmental variability, including temperature ranges.
The United States Department of Defense has defined the United States Military Standard for all products used by the United States Armed Forces. The environmental design and testing limits of a product to the conditions it must undergo throughout its service life are specified in MIL-STD-810 , Department of Defense Test Method Standards for Environmental Engineering Considerations and Laboratory Tests . 
The MIL-STD-810G standard specifies that “Operating temperature stabilization is achieved when the temperature of the working part of the test item with the longest thermal interval is changing at a rate of not more than 2.0 °C (3.6 °F) per hour.” ”  It also specifies procedures for assessing the performance of materials for extreme temperature loads . 
Military engine turbine blades experience two significant deformation stresses during normal service, creep and thermal fatigue .  The creep life of a material is “highly dependent on operating temperature”,  and creep analysis is thus an important part of design validation. Some of the effects of creep and thermal fatigue can be reduced by integrating cooling systems into the design of the device, reducing the extreme temperatures experienced by the metal.
Commercial and retail
Commercial and retail products are manufactured for less stringent requirements than military and aerospace applications. For example, microprocessors produced by Intel Corporation are manufactured in three grades: commercial, industrial, and extended. 
Because some equipment generates heat during operation, they may require thermal management to ensure that they are within their specified operating temperature range; Specifically, that they are operating at or below the maximum operating temperature of the device.  Cooling a microprocessor fitted in a typical commercial or retail configuration requires “a heatsink properly mounted on the processor, and effective air flow through the system chassis”.  The system is designed to protect the processor from abnormal operating conditions, such as “a higher than normal ambient air temperature or failure of a system thermal management component (such as a system fan), Although “an appropriately designed” system, this feature should never be activated”.  Cooling and other heat management techniques can affect performance and noise levels.  Noise mitigation in residential applications Strategies may be needed to ensure that the noise level is not uncomfortable. Battery service life and efficacy are affected by operating temperature.  Capacity is determined by comparing the service life achieved by the battery as a percentage of the service life achieved at 20 °C versus temperature. Ohmic load and operating temperature often jointly determine a battery’s discharge rate.  In addition, if the expected operating temperature for the primary battery deviates from the normal 10 °C to 25 °C, the operating temperature “often will affect the type of battery selected for the application”.  A partially depleted lithium sulfur dioxide battery has been shown to improve energy recovery “when the operating temperature of the battery is raised appropriately”.
Parts of mammalian homeostasis attempt to maintain a comfortable body temperature under various conditions by thermoregulation. A mammal’s lowest normal temperature, basal body temperature, is attained during sleep. In women, it is influenced by ovulation, leading to a biphasic pattern that can be used as a component of fertility awareness.
In humans, the hypothalamus controls metabolism, and therefore basal metabolic rate. Among its functions is the regulation of body temperature. Key body temperature is one of the classic phase markers for measuring the timing of a person’s circadian rhythm.
Discomfort can occur as a result of changes in normal human body temperature. The most common such change is fever, a temporary elevation of the body’s thermoregulatory set-point, usually around 1–2 °C (1.8–3.6 °F). Hyperthermia is an acute condition caused by excess heat being absorbed by the body, whereas hypothermia is a condition in which the core body temperature drops below that required for normal metabolism, and which is unable to replenish body heat. Caused by inability. Being lost to the environment.