比特错误率（英语：bit error ratio, BER）是指一定时间间隔内，传输信号中错误比特的个数对传输的总位数的比值。这物理量可以评估通信系统中数据流受到噪声、干扰、失真等的负面影响。

In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors.

The bit error rate (BER) is the number of bit errors per unit time. The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. BER is a unitless performance measure, often expressed as a percentage.