what are the guns on cruisers

Washington Naval Treaty of 1921 sought to limit an arms race in warships, restricted the construction of all large warships. Among its terms, cruisers could displace no more than 10,000 tons standard and light cruisers could be armed with guns of a calibre not exceeding 6.1 inches (155 mm) guns
By World War I, British light cruisers often had either two 6 inch 152 mm naval guns and perhaps eight 4 inch (100 mm) guns, or a uniform armament of 6 inch 152 mm naval guns on a ship of around 5,000 tons, while German cruisers progressed during the war from 4.1 inch (105 mm) to 5.9 inch (150 mm) guns.

In the London Naval Treaty of 1930, light cruisers were defined as cruisers having guns of 6.1 inch (155 mm) or smaller, with heavy cruisers defined as cruisers having guns of up to 8 inch (203 mm). In both cases, the ships could not be greater than 10,000 tons
In the World War II era, light cruisers had guns ranging from 5 inch (127 mm), as seen in the Atlanta-class anti-aircraft cruiser, to 6.1 inch, though the most common size by far was 6 inch. Heavy cruisers usually had a battery of 8 inch (203 mm) guns. Armament based on 6-inch (152 mm) guns was considered to be superior to that using 8-inch 203 mm naval guns. The former fired faster and more of them could be carried for the same weight as for the 8 inch. The heavier shell of the 8 inch was little advantage because ships that could withstand a 6 inch hit were well-protected against 8 inch shells, though only the US 6-inch and the Japanese 6.1-inch (155 mm) guns had the power to reliably penetrate treaty-cruisers