Alloy Composition Calculator
Convert between atomic percent and weight percent, calculate theoretical batch quantities, and save compositions for your next experiment.
Step 1 Define composition
Select elements by name or symbol. Enter percentages on the input basis below.
Input: at% · Output: wt%
Values are never silently rescaled. Results require a total of 100%.
Step 2 Results
THEORETICALBoth at% and wt% are reported. Mass is calculated from wt%.
| Element | at% | wt% | Mass (g) |
|---|---|---|---|
| Total | 100 | 100 |
Displayed values are rounded to 6 decimal places. Calculations, JSON and CSV retain numerical precision.
Add your elements and percentages, or load the equiatomic CoCrFeMnNi example to begin.
Theoretical batch masses do not account for raw-material purity, manufacturing losses or volatilization. Results do not represent the final product composition and do not predict alloy phases or properties.
Step 3 Save & share
Saved in this browser. Export a copy to keep or share your compositions.
Share links contain the full composition and batch mass. Do not use them for confidential compositions. Anyone with the link can read the recipe.
Step 4 Request a material review
Send this composition with your requirements. Manufacturability, specifications and lead time are reviewed by our team during quotation.
Your composition is carried to the existing quote form in this browser tab. Contact details are collected there. Nothing is sent until you submit the inquiry.
How the conversion works
Atomic percent (at%) describes the proportion of atoms; weight percent (wt%) describes the proportion of mass. For each element i, Mi is its atomic weight. With percent inputs, the conversion formulas are:
Atomic → weightwt%i = 100 × (at%i × Mi) / Σ(at%j × Mj)
Weight → atomicat%i = 100 × (wt%i / Mi) / Σ(wt%j / Mj)
Each theoretical elemental mass equals the total batch mass multiplied by that element’s weight fraction. The example uses Co, Cr, Fe, Mn and Ni at 20 at% each; their weight percentages are different.
Atomic-weight data
Source: CIAAW / IUPAC Abridged Standard Atomic Weights 2024, based on the Atomic Weights 2021 report with 2024 revisions; data snapshot checked October 8, 2026. The calculator uses the table’s published central values, not isotope masses or invented interval midpoints. The published values are abridged; internal numerical precision does not increase their scientific accuracy.
Natural isotopic variation and the table’s uncertainties are not propagated here. Isotopically enriched feedstocks require a different mass model. 84 elements are supported; 34 elements without a standard atomic weight, including technetium and promethium, are marked unsupported.
Common questions
Why is an equiatomic alloy not equal weight percent?
Equal atomic fractions contain equal numbers of atoms, but elements have different atomic weights. Heavier elements contribute more mass for the same number of atoms.
What if my input does not add up to 100%?
The total is shown as you type. Results remain unavailable until you correct the total or explicitly choose Normalize to 100%. Normalization rescales each input in proportion to its original value; it never runs silently.
Where are my saved compositions stored?
They stay in localStorage in this browser profile, without an account or external database. Clearing site data removes them. Export JSON for backup. Calculation inputs are not sent to analytics; the public tool page does not load the storefront analytics bootstrap.
Does this establish an alloy specification or guarantee supply?
No. It is a theoretical planning tool. Final composition, processing feasibility, purity, losses, dimensions, documentation and lead time require material-specific review.