Sevenoaks Tunnel is 1 mile 1,691 yards long and built of clay and greensand, completely lined with brickwork of varying thicknesses. 276,000 square yeards of material were removed during its construction.

The tunnel arch is 25ft high and horseshoe shaped, being 24ft 8in wide at its base. The tracks stand at about 4ft 6in above the brick-lined invert. Construction required 15 working shafts, varying in depth from 116ft to 394ft.

The tunnel slopes gently downhill towards Tonbridge.