Fiber artifacts of very well measured lengths are required for the calibration of optical time-domain reflectometers (OTDR). In this paper, accurate length measurement of different fiber lengths using the time-of-flight technique is performed. A setup is proposed to measure accurately lengths from 1 km to 40 km at 1550 nm and 1310 nm using a high speed electro-optic modulator, a photodetector and a time interval counter (TIC). This setup offers traceability to the SI unit of time, the second, (and hence to the meter by definition) by locking the time interval counter to the GPS-disciplined quartz oscillator. Additionally, the length of a recirculating loop artifact is measured and compared with the measurement made for the same fiber by the National physical laboratory of United Kingdom (NPL). Finally, a method is proposed to relatively correct the fiber refractive index to allow accurate fiber length measurement.