Exodus 25:17 New English Translation

¹⁷“You are to make an atonement lid^[a] of pure gold;^[b] its length is to be 45 inches, and its width is to be 27 inches.

Exodus 25:17 tn The noun is כַּפֹּרֶת (kapporet), translated “atonement lid” or “atonement plate.” The traditional translation “mercy-seat” (so KJV, ASV, NASB, NRSV) came from Tyndale in 1530 and was also used by Luther in 1523. The noun is formed from the word “to make atonement.” The item that the Israelites should make would be more than just a lid for the ark. It would be the place where atonement was signified. The translation of “covering” is probably incorrect, for it derives from a rare use of the verb, if the same verb at all (the evidence shows “cover” is from another root with the same letters as this). The value of this place was that Yahweh sat enthroned above it, and so the ark essentially was the “footstool.” Blood was applied to the lid of the box, for that was the place of atonement (see S. R. Driver, Exodus, 269-270).
Exodus 25:17 tn After verbs of making or producing, the accusative (like “gold” here) may be used to express the material from which something is made (see GKC 371 §117.hh).

New English Translation (NET)