A radial tire for an aircraft, the radial tire having a rim diameter of 20 inches or less, the radial tire comprising: a pair of bead portions; a pair of sidewall portions extending outward from the bead portions in a substantially radial direction; a tread portion that couples together respective radial outer ends of the sidewall portions; a toroidal carcass layer reinforcing a portion between bead cores embedded in the bead portions; and a belt layer and a tread that are sequentially laminated on an outer side of the carcass layer in the radial direction, wherein a value M obtained by dividing a tire external diameter D by a distance L between bead heels of the bead portions is in a range of from 4.1 to 5.4, characterised in that in a case in which A represents an intersection between an internal surface edge in a tire meridional cross section and a normal N that is normal relative to the carcass layer and passes through a tread ground contact end E that refers to an outermost ground contact position of a ground contact region on a road in a tire axial direction, provided that the tire is attached to a standard rim of an applicable size described in a standard TRA "Aircraft Year Book of the Tire and Rim Association Inc." effective in the U.S.A., is filled with a standard internal pressured defined in the standard TRA and is applied with a standard load defined in the standard TRA, B represents a length between a tire equator S and the intersection A along the carcass layer, C represents a radius of curvature of the internal surface edge at the tire equator S, and J represents a radius of curvature of the internal surface edge between the intersection A and a point H that is distanced 0.84 times the length B apart from the tire equator S, a value G obtained by dividing the radius of curvature J by the radius of curvature C is in a range of from 0.152 to 0.166. a pair of bead portions; a pair of sidewall portions extending outward from the bead portions in a substantially radial direction; a tread portion that couples together respective radial outer ends of the sidewall portions; a toroidal carcass layer reinforcing a portion between bead cores embedded in the bead portions; and a belt layer and a tread that are sequentially laminated on an outer side of the carcass layer in the radial direction, wherein a value M obtained by dividing a tire external diameter D by a distance L between bead heels of the bead portions is in a range of from 4.1 to 5.4, characterised in that in a case in which A represents an intersection between an internal surface edge in a tire meridional cross section and a normal N that is normal relative to the carcass layer and passes through a tread ground contact end E that refers to an outermost ground contact position of a ground contact region on a road in a tire axial direction, provided that the tire is attached to a standard rim of an applicable size described in a standard TRA "Aircraft Year Book of the Tire and Rim Association Inc." effective in the U.S.A., is filled with a standard internal pressured defined in the standard TRA and is applied with a standard load defined in the standard TRA, B represents a length between a tire equator S and the intersection A along the carcass layer, C represents a radius of curvature of the internal surface edge at the tire equator S, and J represents a radius of curvature of the internal surface edge between the intersection A and a point H that is distanced 0.84 times the length B apart from the tire equator S, a value G obtained by dividing the radius of curvature J by the radius of curvature C is in a range of from 0.152 to 0.166.