We explore the potential of the electric quadrupole transitions 7s 2 S 1/2 -6d 2 D 3/2 , 6d 2 D 5/2 in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive A Ra + candidates, with A = 223-229, are identified. In particular, we show that the transition 7s 2 S 1/2 (F = 2,m F = 0)-6d 2 D 3/2 (F = 0,m F = 0) at 828 nm in 223 Ra + , with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of 10 −17 . With more experimental effort, the 223,225,226 Ra + clocks could be pushed to a projected performance reaching the 10 −18 level.