  We present the accretion disk size estimates for a sample of 19 active
galactic nuclei (AGN) using the optical $g$, $r$, and $i$ band light curves
obtained from the Zwicky Transient Facility (ZTF) survey. All the AGN have
reliable supermassive black hole (SMBH) mass estimates based on previous
reverberation mapping measurements. The multi-band light curves are
cross-correlated, and the reverberation lag is estimated using the Interpolated
Cross-Correlation Function (ICCF) method and the Bayesian method using the {\sc
javelin} code. As expected from the disk reprocessing arguments, the $g-r$ band
lags are shorter than the $g-i$ band lags for this sample. The interband lags
for all, but 5 sources, are larger than the sizes predicted from the standard
Shakura Sunyaev (SS) analytical model. We fit the light curves directly using a
thin disk model implemented through the {\sc javelin} code to get the accretion
disk sizes. The disk sizes obtained using this model are on an average 3.9
times larger than the prediction based on the SS disk model. We find a weak
correlation between the disk sizes and the known physical parameters, namely,
the luminosity and the SMBH mass. In the near future, a large sample of AGN
covering broader ranges of luminosity and SMBH mass from large photometric
surveys would be helpful in a better understanding of the structure and physics
of the accretion disk.
