Alloy Composition Calculator

Example data table

Use the calculator to convert these weight values into atomic composition.

Formula used

• Mass to moles: n_i = m_i / M_i
• Weight percent: wt%_i = 100 × m_i / Σm
• Atomic percent: at%_i = 100 × n_i / Σn
• Average molar mass: M̄ = Σm / Σn
• Mixture density (rule of mixtures): ρ = Σm / Σ(m/ρ_i)

Atomic percent is based on mole fraction, which matches atom fraction for elements.

How to use this calculator

1. Select an input method: masses, moles, or weight percent.
2. Enable at least two components and choose each material.
3. Enter the amount field that matches your chosen method.
4. For custom entries, provide molar mass and optional density.
5. Click Calculate to see totals and both composition bases.
6. Use the download buttons to export CSV or PDF results.

Professional article

1) Why alloy composition control matters

Small changes in chemistry can shift phase balance, corrosion response, and strength. This calculator helps you compare weight and atomic bases, so a specification like 18 wt% chromium can be translated into atomic percent for diffusion, oxidation, and thermodynamic discussions.

2) Weight percent versus atomic percent

Weight percent reflects mass contribution and is common in purchasing and melt practice. Atomic percent reflects the number of atoms and is preferred for lattice occupancy, point-defect models, and reaction stoichiometry. Because molar masses differ widely, wt% and at% can look very different.

3) Converting from mass and moles

When you enter masses, the calculator converts each component to moles using n = m/M. Mole fractions then follow from n/Σn, and atomic percent is 100×(n/Σn). The same workflow works in reverse if you start from moles.

4) Working with weight percent inputs

Percent entries are useful when you already have a target recipe. If your inputs do not sum to 100, normalization rescales them while keeping relative ratios. You can also set a basis mass, such as 100 g or 5 kg, to compute component masses and moles consistently.

5) Average molar mass and what it indicates

The average molar mass M̄ = Σm/Σn provides a compact descriptor for mixed compositions, useful in gas-equivalent conversions, mass-to-atom scaling, and quick checks during calculations. For many alloy systems, M̄ changes smoothly with composition and reveals heavy-element enrichment.

6) Estimating mixture density by rule of mixtures

Density is estimated with a volume-based rule of mixtures: ρ = Σm / Σ(m/ρi). This assumes ideal volume additivity and is best for quick screening. Measured densities can differ due to porosity, ordering, or non-ideal packing, especially in multiphase systems.

7) Data quality and practical limits

Accurate molar masses and consistent units are critical. Trace additions like carbon or boron may be small by mass but large by atomic percent. For compounds or phases, use the custom option with an effective molar mass, and treat results as an informative approximation.

8) Typical workflows in labs and production

Metallurgy labs often measure composition by weight and then convert to atomic percent for modeling. Production teams may start with a wt% specification, choose a basis mass, and compute charge weights. This tool supports both workflows, exports results, and reduces manual errors. Include trace elements carefully, because rounding can hide meaningful atomic fraction shifts in sensitive alloys.

FAQs

1) What is the difference between wt% and at%?

Weight percent is based on mass. Atomic percent is based on mole fraction, which matches atom fraction for elements. Heavy elements can dominate wt% while contributing fewer atoms.

2) When should I normalize percentages?

Normalize when your entered percentages represent a recipe but do not sum to 100 due to rounding or partial reporting. Normalization preserves ratios and scales the set to 100%.

3) Can I model a compound or phase instead of an element?

Yes. Choose “Custom” and enter an effective molar mass for the phase. If you know an effective density, add it to improve the mixture density estimate.

4) Why does atomic percent change so much for light elements?

Light elements have low molar mass, so a small mass can represent many moles. That boosts mole fraction and atomic percent even when wt% looks minor.

5) Is the mixture density always accurate?

No. The rule of mixtures assumes ideal volume additivity. Real alloys may deviate because of porosity, ordering, thermal expansion differences, or multi-phase microstructures.

6) What basis mass should I use for wt% inputs?

Use 100 g for easy interpretation, or match your batch size, such as 5000 g. The chosen basis scales component masses and moles while keeping the same wt% and at%.

7) How many components can I include?

You can add as many rows as needed. For stability, keep only relevant components enabled and ensure each enabled row has valid input for the selected method.

FAQs

1) What is the difference between wt% and at%?

Weight percent is based on mass. Atomic percent is based on mole fraction, which matches atom fraction for elements. Heavy elements can dominate wt% while contributing fewer atoms.

2) When should I normalize percentages?

Normalize when your entered percentages represent a recipe but do not sum to 100 due to rounding or partial reporting. Normalization preserves ratios and scales the set to 100%.

3) Can I model a compound or phase instead of an element?

Yes. Choose “Custom” and enter an effective molar mass for the phase. If you know an effective density, add it to improve the mixture density estimate.

4) Why does atomic percent change so much for light elements?

Light elements have low molar mass, so a small mass can represent many moles. That boosts mole fraction and atomic percent even when wt% looks minor.

5) Is the mixture density always accurate?

No. The rule of mixtures assumes ideal volume additivity. Real alloys may deviate because of porosity, ordering, thermal expansion differences, or multi-phase microstructures.

6) What basis mass should I use for wt% inputs?

Use 100 g for easy interpretation, or match your batch size, such as 5000 g. The chosen basis scales component masses and moles while keeping the same wt% and at%.

7) How many components can I include?

You can add as many rows as needed. For stability, keep only relevant components enabled and ensure each enabled row has valid input for the selected method.