A megahertz (MHz) is one million (10⁶) hertz, a measure of frequency.

In radio, many frequencies fall into the MHz range:

• LF (Low Frequency) 0.03 - 0.3 MHz
• MF (Medium Frequency) 0.3-3 MHz
• HF (High Frequency) 3-30 MHz
• VHF (Very High Frequency) 30 - 300 MHz
• UHF (Ultra High Frequency) 300 - 1000 MHz

In computing, most CPUss are labelled in terms of megahertz. This refers to the cycle frequency of the CPU's "master" clock. If two otherwise identical CPUs have different "clock speeds", the one with the higher clock speed (larger megahertz) will be faster than the other. In practice, many other factors influence the performance of computers, and consumers are advised to place little store on this factor when purchasing a computer. For example, a RISC processor, which has very small instructions that can be accomplished quickly, may run at a higher clock rate (at higher MHz) than a CISC processor with large instructions, but because the CISC processor accomplishes more during each clock, it may be faster for any real-world application. If performance is important, more detailed information than a MHz rating is required to make an informed decision. See benchmark for further discussion of computer performance comparisons.

Note: many computers now have clock frequencies above 1000 MHz, and their clock frequencies are now quoted in gigahertz (10⁹ hertz): so an 1800 MHz clock frequency is referred to as 1.8 GHz.