Gold Alloy & Karat Adjustment Calculator
Enter a known starting mass and karat to calculate the ideal addition needed for your target. Review the resulting metal mass, gold content and worked steps.
Enter your values or load an example. Calculations stay in this browser.
Use a known metal composition
Karat expresses the gold fraction in 24 parts by mass: 18K represents 18/24, or 75% gold. Enter the mass of the metal itself, excluding stones and other attached materials. A photo or uncertain stamp does not establish the composition.
Raise karat by adding fine gold
The higher-karat calculation assumes the addition is ideal pure gold, represented as 24K. For 10 g of 14K starting metal and an 18K target, the ideal addition is 6.6666667 g of fine gold. The final mixture is approximately 16.6666667 g.
Lower karat with gold-free alloy
To lower 10 g of 18K metal to 14K, the ideal model adds approximately 2.8571429 g of gold-free alloy metal. Gold content stays at 7.5 g while total mass increases. The calculation does not choose the alloy ingredients.
Check the conservation of mass
For starting mass M, starting karat S, target T and addition karat A, added mass is M × (T − S) / (A − T). This follows by setting (M × S + added mass × A) / (M + added mass) equal to T. The tool uses A = 24 when raising karat and A = 0 when lowering it.
Know the limits of an ideal calculation
An impure starting alloy cannot reach exactly 24K by adding a finite mass of fine gold. Equal starting and target karats need no addition. Real material losses, assay tolerances and alloy compatibility require a qualified jeweller's assessment. No processing recipe or price is provided.
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Frequently Asked Questions
How much fine gold raises 10 g of 14K to 18K?
Under the ideal model, add approximately 6.6666667 g of pure gold. The final mass is approximately 16.6666667 g at 18K, assuming no losses.
Can I reach pure 24K by adding gold to 18K?
Not exactly with a finite addition. The original non-gold metal remains in the mixture. Choose a target below 24K for this calculator.
What if the starting and desired karats are the same?
The required addition is zero and the final mass equals the starting mass.
Does the result specify a jewelry alloy recipe?
No. It calculates gold mass balance only. Color, hardness and material compatibility depend on the other metals and are not determined here.
Can I use plated or gold-filled weight?
Not as a homogeneous karat alloy. A coating or bonded layer has a different composition from its core. Use a documented composition and metal mass appropriate to the calculation.
Continue in the app
Explore photo identification features in Gold Detector - Goldiva. The calculator above uses only the values you enter.
