Metal.               Cost per ibs

Platinum.         500gp

Gold                  50gp

Electrum.          25gp 

Silver.                5gp

Copper.             5sp

Steel.                 4sp

Bronze.              4sp

Cold iron.           4sp

Brass.                  3sp 

Tin.                     3sp

Lead.                 2sp

Iron.                  1sp

This all my opinion if you have any questions please contact me.

ENJOY

Your forgot adamantite, often considered the best metal.

This appears to have been pulled verbatim (and incompletely) from Volo's Guide to All Things Magical. So, if you would like the complete list, I recommend that official source.

• 500 iron pieces = 1 gp
• 1 adamantine piece = 2 gp
• 1 mithral piece = 1 gp

These three sources establish the value of gold per pound and that the value of coin quantity to pure metal quantity is flat (there's no 'value added' by making the coin).

• Player Handbook, Chapter 5: "A standard coin weighs about a third of an ounce, so fifty coins weigh a pound."
• Player's Handbook, Chapter 5: "50 gp = 1 lb. of gold"
• Player's Handbook, Chapter 5: "... Rather, the gold piece is a standard measure of value, and the actual exchange is in gold bars..."

These sources establish the exchange rates for the metals not included in the original PHB chart (iron, mithral, and adamantine).

• Iron: Player's Handbook, Chapter 5: "1 sp = 1 lb. of iron". Dungeon Master's Guide, Chapter 1: "...iron is normally valued elsewhere (1 sp per pound)."
• Adamantine: Waterdeep: Dragon Heist, Chapter 4: "The characters can purchase a 10-pound adamantine bar for 1,000 gp." (this sets the price of 1 pound of adamantine equal to 2 pounds of gold)

• Mithral: Waterdeep: Dungeon of the Mad Mage, Chapter 6: "One character can strip 1 pound of mithral in 15 minutes. Each pound of the metal is worth 50 gp." (this sets the price of 1 pound of mithral equal to 1 pound of gold)

The mithral and adamantine prices are also confirmed on this tweet, which unfortunately doesn't make it clear that he's talking about pounds.

Having said all that, Tomb of Annihilation, Chapter 2 has a very different price for adamantine. "Each adamantine ingot is worth 10 gp and weighs 1 pound." So here, 1 gp = 5 adamantine pieces (adamantine is significantly cheaper than gold in this section). It does say the ingots are "refined adamantine". I think its easy to explain this off as local market dynamics (a 'nonstandard' exchange rate) or the fact that these specific ingots aren't fully refined. Also note that Tomb of Annihilation doesn't have this regional pricing adjustment for iron as the exchange rate is that listed in the chart above "each iron ingot is worth 1 gp and weights 10 pounds).

Thank you for this it is supper helpful

How much copper would it take to plate a 5'x5' floor section, say the thickness of a coin or perhaps half that???

3 lbs = 1 square foot at a thickness of .0647"  A US penny is .06"

75 pounds of copper is need to cover a 5x5 space.

Thank you. Building a Bastion and plating a hallway as a trap/defense. 😁