Yashima was 412 feet (125.6 m) long overall and had a beam of 73 feet 6 inches (22.4 m) and a full-load draught of 26 feet 3 inches (8.0 m). She normally displaced 12,230 long tons (12,430 t) and had a crew of 650 officers and enlisted men. Unlike her sister ship Fuji, she was fitted as an admiral's flagship.
The ship was powered by two vertical triple-expansion steam engines using steam generated by ten cylindrical boilers. The engines were rated at 13,500 indicated horsepower (10,100 kW), using forced draught, and designed to reach a top speed of 18.25 knots (33.80 km/h; 21.00 mph). Yashima, however, reached a top speed of 19.46 knots (36.04 km/h; 22.39 mph) from 14,075 ihp (10,496 kW) on her sea trials. She carried a maximum of 1,200 tonnes (1,200 long tons) of coal which allowed her to steam for 4,000 nautical miles (7,400 km; 4,600 mi) at a speed of 10 knots (19 km/h; 12 mph).[Note 1]
Yashima's main battery consisted of four 12-inch (305 mm) guns mounted in two twin gun turrets, one each fore and aft of the superstructure. The secondary battery consisted of ten 6-inch (152 mm) quick-firing guns, four mounted in casemates on the sides of the hull and six mounted on the upper deck, protected by gun shields. A number of smaller guns were carried for defence against torpedo boats. These included fourteen 47-millimetre (1.9 in) 3-pounder guns and ten 2.5-pounder Hotchkiss guns of the same calibre.[Note 2] She was also armed with five 18-inch torpedo tubes. Yashima's waterline armour belt consisted of Harvey armour and was 14–18 inches (356–457 mm) thick. The armour of her gun turrets was six inches thick and her deck was 2.5 inches (64 mm) thick.
In 1901, the ship exchanged 16 of her 47 mm guns for an equal number of QF 12 pounder 12 cwt[Note 3] guns. This raised the number of crewmen to 652 and later to 741.