Scatterer size estimation is useful when characterizing tissue using ultrasound. In all previous studies on scatterer size, the estimations are performed in the frequency domain and are thus subjected to a trade off in time-frequency resolution. This study focused on the feasibility of estimating scatterer size in the time domain using only the ultrasound center frequency, assuming a Gaussian-shaped pulse. A model for frequency normalization was derived and the frequency-dependent attenuation was compensated. Five phantoms with well-defined sizes of spherical glass beads were made and scanned with two different linear array transducers with variable center frequencies. A strong correlation (r = 0.99, p < 10-19) between the backscattered center frequency and the product between the wave number and scatterer radius was demonstrated. On average the scatterer diameter was underestimated by 6% ± 24%. These results suggest that estimation of scatterer size is possible using only the center frequency assessed in the time domain.