I was reading recently about ancient Korean artillery, as one does, and the largest ship-mounted cannon at the time of Yi Sun-Sin was the Cheongja. In the Yungwon Pilbi, its dimensions are recorded, and they work out to a length of 1.4 meters (4.59 feet), caliber 118 millimeters (4.65 inches), weight 725 kilograms(1,598.35 pounds), and a powder charge of 1,125 grams (2.48 pounds).
A 12-pounder cannon has a caliber of 4.65 inches. The weight's fairly close, at 1,587.8 pounds, but the cannon is much longer (6.98 feet) and uses more than twice as much powder (6 pounds). The "standard" 12 pounder does 4d10 damage and has a short range of 209.4 yards (obviously, without rounding). Simply making the two changes (and ignoring the subsequent effect on weight), a Cheongja would end up doing 3d10 damage with a short range of 137.7 yards and long range of 667.8 yards.
The next largest cannon was the Jija, at 47.24 inches long, 4.13 inches in caliber, a weight of 956.81 pounds, and a powder charge of 1.65 pounds. This works out to an 8.2-pdr cannon, although it's lighter (a standard 8.2-pdr would be 1109 pounds). After shortening it and adjusting the charge, it becomes a cannon that does 2d10 damage with a short range of 118.1 yards and long range of 572.8 yards.
After the Jija was the Hyeonja, which was 35.43 inches long, 2.40 inches in caliber, 205.03 pounds, and used only 0.33 pounds of powder per shot. This ends up being a 1.4-pdr cannon, which would normally weight 218.03 pounds, so we're still fairly close on weight despite the Korean cannon being short and lightly charged. After adjustments, it does 1d10 with a short range of 88.6 yards and long range of 429.6 yards.
Lastly comes the diminutive Hwanja, at 31.5 inches long, 1.81 inches in caliber, 171.96 pounds, and 0.25 pounds of powder. This is a 0.53-pdr, and is actually much less efficient than the cannon formula would project, since a GoW .53-pdr weighs only 92.9 pounds and uses 0.265 pounds of powder (and is 32.52 inches long). The adjustments end up being minimal, and the Hwanja fires a 1d10 projectile to a short range of 78.8 yards and a long range of 381.9 yards.
Admiral Yi wrote of testfiring the Jija and Hyeonja of a new ship he was building, the geobukseon (turtle ship), which was a rowed ship with iron spikes on the roof to discourage boarding. His nephew, Yi Bun, recorded that they had five or six "fire holes" on each side, presumably the gunports for cannon. There were also a few (2-3) gunports facing fore and aft. There are arguments about precisely which type of cannon was carried where. The most likely (to me) is that it carried jija broadsides or alternating jija and hyeonja, with a single cheongja forward flanked by a pair of hyeonja, and possibly the same aft.