Taking as a postulate that "space undergoes right-handed cylindrical helical motion at the speed of light c," this paper presents a geometric formulation of electric charge. The helix angle θ is defined as the angle between the tangent and the helix axis; it describes how the speed of light is partitioned between the azimuthal and axial directions. The fine-structure constant is the sine of the helix angle, α = sin θ, with θ = 0.41811°, and the path ratio is Ω = csc θ = 1/α. With c and the helix radius r held fixed, the helix angle θ is the sole degree of freedom of the helix. Treating Gεu2080 as a single entity, termed the space-time coupling baseline, and adopting the ratio of geometric coefficients k/ku2032 = Ω²c² as the fundamental relation, local energy balance yields Gεu2080(α) = α²/c². Taking the first derivative with respect to the geometric quantity sin θ of the helix angle gives the charge formula q = d(Gεu2080)/d(sin θ) = 2α/c². Spatial helices are uniformly right-handed; the helical flow of a positive charge is outward-diverging, whereas that of a negative charge is inward-converging. The total charge is Q = nq, where n is the helical winding number; the number and the sign of charges are topological invariants, while the magnitude q of each unit is bound to α. Numerically, G = μu2080α² deviates from the experimental G by 0.2616%, five times which is 1.3082%, whereas 2α/c² deviates from the elementary charge e by 1.3546%; the two differ by 0.046 percentage points. The charge formula gives q ∝ α; as α runs from its low-energy value 1/137.036 to 1/127.930 at the Z-boson energy scale, the unit charge q increases by 7.12%, which is consistent with the strengthening of the electromagnetic interaction at high energies. On this basis, one falsifiable prediction and one testable conjecture are proposed: the prediction is that an accelerating positive charge produces an induced gravitational field directed opposite to its acceleration; the conjecture is that secondary H and He fragments traversing the Bragg peak region of carbon ions exhibit velocity and stopping anomalies.