  We study the band gap of finite $N_A=7$ armchair graphene nanoribbons
(7-AGNRs) on Au(111) through scanning tunneling microscopy/spectroscopy
combined with density functional theory calculations. The band gap of 7-AGNRs
with lengths of 6 nm and more is converged to within 0.1 eV of its bulk value
of 2.3 eV, while the band gap opens by several hundred meV in very short
7-AGNRs. The termination has a significant effect on the band gap, doubly
hydrogenated termini yielding a lower band gap than singly hydrogenated ones.
