The demi-culverin was a medium cannon

Cannon

A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...

 similar to but slightly larger than a saker

Saker (cannon)

The saker was a medium cannon slightly smaller than a culverin developed during the early 16th century and often used by the English. It was named after the Saker Falcon, a large falconry bird native to the Middle East....

 and smaller than a regular culverin

Culverin

A culverin was a relatively simple ancestor of the musket, and later a medieval cannon, adapted for use by the French in the 15th century, and later adapted for naval use by the English in the late 16th century. The culverin was used to bombard targets from a distance. The weapon had a...

 developed in the early 17th century. Barrels of demi-culverins were typically about 11 feet (3.4 m) long, had a calibre of 4 inches (10.2 cm) and could weigh up to 3400 pounds (1,542.2 kg). It required 6 pounds (2.7 kg) of black powder to fire an 8 pounds (3.6 kg) round shot (though there were heavier variants firing 9 pounds (4.1 kg) or 10 pounds (4.5 kg) round shot). The demi-culverin had an effective range of 1800 feet (548.6 m).

Demi-culverins were valued by generals for their range, accuracy and effectiveness. They were often used in sieges for wall and building demolition.