The Léon Gambetta-class ships were designed as enlarged and more powerful versions of the Gloire-class armored cruisers.
The first two ships (Léon Gambetta and Jules Ferry) measured 148.35 meters (486 ft 9 in) overall, with a beam of 21.4 meters (70 ft 3 in) and a draft of 8.18 meters (26 ft 10 in).
All three sister ships were designed to displace 12,550 metric tons (12,352 long tons) at normal load.
Their crew normally numbered 26 officers and 708 enlisted men, or 30 officers and 749 men when serving as a flagship.

The ships had three vertical triple-expansion steam engines, each driving one propeller shaft.
Each of the sisters used a different model of water-tube boiler and Jules Ferry was fitted with 20 Guyot-du Temple boilers.
Their engines were rated at a total of 27,500 metric horsepower (20,200 kW) to reach their designed speed of 22 knots (41 km/h; 25 mph).
During her sea trials on 7 December 1906, Jules Ferry reached 22.6 knots (41.9 km/h; 26.0 mph) from 28,743 metric horsepower (21,140 kW).
The cruisers carried enough coal to give them a range of 7,500 nautical miles (13,900 km; 8,600 mi) at a speed of 10 knots (19 km/h; 12 mph).

The main battery of the Léon Gambetta class consisted of four 194-millimeter Modèle 1893–1896 guns mounted in twin-gun turrets fore and aft of the superstructure.
Their secondary armament comprised sixteen 164-millimeter (6.5 in) Modèle 1893–1896M guns.
Twelve of these were in three twin-gun turrets on each broadside and the remaining four guns were in casemates in the hull.
For defense against torpedo boats, they carried twenty-four 47-millimeter (1.9 in) Hotchkiss guns.
Jules Ferry was also armed with two submerged 450-millimeter (17.7 in) torpedo tubes, one on each broadside, and could carry 10 naval mines.

The cruisers' waterline armor belt ranged in thickness from 80 to 150 millimeters (3.1 to 5.9 in) and the main-gun turrets were protected by armor 138 millimeters (5.4 in) thick.
Their deck armor was 33 to 65 mm (1.3 to 2.6 in) thick.
The front and sides of the conning tower consisted of 174-millimeter (6.9 in) armor plates.
The Léon Gambetta-class ships were designed as enlarged and more powerful versions of the Gloire-class armored cruisers. The first two ships (Léon Gambetta and Jules Ferry) measured 148.35 meters (486 ft 9 in) overall, with a beam of 21.4 meters (70 ft 3 in) and a draft of 8.18 meters (26 ft 10 in). All three sister ships were designed to displace 12,550 metric tons (12,352 long tons) at normal load. Their crew normally numbered 26 officers and 708 enlisted men, or 30 officers and 749 men when serving as a flagship.
The ships had three vertical triple-expansion steam engines, each driving one propeller shaft. Each of the sisters used a different model of water-tube boiler and Jules Ferry was fitted with 20 Guyot-du Temple boilers. Their engines were rated at a total of 27,500 metric horsepower (20,200 kW) to reach their designed speed of 22 knots (41 km/h; 25 mph). During her sea trials on 7 December 1906, Jules Ferry reached 22.6 knots (41.9 km/h; 26.0 mph) from 28,743 metric horsepower (21,140 kW). The cruisers carried enough coal to give them a range of 7,500 nautical miles (13,900 km; 8,600 mi) at a speed of 10 knots (19 km/h; 12 mph).
The main battery of the Léon Gambetta class consisted of four 194-millimeter Modèle 1893–1896 guns mounted in twin-gun turrets fore and aft of the superstructure. Their secondary armament comprised sixteen 164-millimeter (6.5 in) Modèle 1893–1896M guns. Twelve of these were in three twin-gun turrets on each broadside and the remaining four guns were in casemates in the hull. For defense against torpedo boats, they carried twenty-four 47-millimeter (1.9 in) Hotchkiss guns. Jules Ferry was also armed with two submerged 450-millimeter (17.7 in) torpedo tubes, one on each broadside, and could carry 10 naval mines.
The cruisers' waterline armor belt ranged in thickness from 80 to 150 millimeters (3.1 to 5.9 in) and the main-gun turrets were protected by armor 138 millimeters (5.4 in) thick. Their deck armor was 33 to 65 mm (1.3 to 2.6 in) thick. The front and sides of the conning tower consisted of 174-millimeter (6.9 in) armor plates.
French cruiser Jules Ferry