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Karat Adjustment Calculator

Calculate how much alloy or pure gold to add to convert gold from one karat to another.

Gold & Silver

Karat Adjustment Calculator

Generated on April 24, 2026

Adding material at 24K (100.00% pure). Auto mode picks pure gold when upgrading and pure alloy when downgrading.

?What is the Karat Adjustment Calculator?

A karat adjustment calculator solves a practical jewellery-workshop problem: you have X weight of Y-karat gold, and you want to end up with Z-karat gold — how much metal do you need to add, and what type? If you're downgrading karat (e.g., 24K → 22K to make jewellery more durable), you add pure alloy. If you're upgrading (e.g., 18K → 22K for higher purity), you add pure 24K gold. The calculator handles both directions automatically, shows the exact amount to add in all units, and verifies the resulting purity. It's used by working jewellers, goldsmith apprentices, and anyone melting down old jewellery to recast at a different karat.

The Formula

Weight to add = Current Weight × (K_target − K_current) ÷ (K_added − K_target).

This generalized formula handles both downgrading (adding alloy) and upgrading (adding pure gold). When downgrading, K_target < K_current and you typically add 0K alloy, so the denominator becomes negative, the numerator is negative, and the quotient is positive — the amount of alloy to add. When upgrading, K_target > K_current and you add 24K gold; both numerator and denominator are positive. The calculator auto-selects 24K or 0K based on direction, but also supports a custom karat in case you're combining gold of a specific intermediate karat (e.g., melting 22K old stock into 18K new).

Practical Examples

1

Have 10 tola of 24K pure gold, want to convert to 22K: alloy to add = 10 × (22 − 24)/(0 − 22) = 0.909 tola of alloy; new total 10.909 tola of 22K.

2

Have 10 tola of 18K, want to convert to 22K: pure 24K to add = 10 × (22 − 18)/(24 − 22) = 20 tola of pure gold; new total 30 tola of 22K.

3

Have 50 g of 22K, want 21K (Middle Eastern grade): alloy to add = 50 × (21 − 22)/(0 − 21) = 2.38 g alloy; new total 52.38 g.

4

Have 100 g of 14K, want to upgrade to 18K for resale: 24K to add = 100 × (18 − 14)/(24 − 18) = 66.67 g pure gold; new total 166.67 g of 18K.

5

Mixing scenarios: Have 20 g of 22K and 30 g of 18K — what's the combined karat? Use Weight Arithmetic & Purity calculators together.

6

Cannot upgrade 18K to 24K by adding 22K gold: denominator (22 − 24) is negative while numerator (24 − 18) is positive → the calculator warns that this combination is geometrically impossible.

Frequently Asked Questions

Because adding 24K gold to 24K gold keeps the mixture 24K — you can't reduce purity by adding more of the same purity. To reduce karat, you must add alloy metal (0K material or lower-karat gold). This is the same reason you can't make salt water fresher by adding more salt water — you need to add fresh water.

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