Engineering Calculators

Quick reactor-physics conversions for material cards and criticality bookkeeping. All math runs in your browser; nothing is sent to a server.

Enter element symbols (e.g. U, O) or Z numbers and their fractions. Results update in real time.

NuclideAtom Frac

N = ρ · N_A / M · f — convert mass density to number density.

Presets:

Density (g/cm³)

Molar Mass (g/mol)

Packing Fraction

MCNP uses negative mass density (g/cm³) or positive number density (atoms/barn-cm). Convert between them for a single-species material.

Mass density (g/cm³)

Molar mass (g/mol)

Packing fraction

ρ = (k − 1) / k; pcm = ρ × 10⁵. Enter any one quantity to get the others.

k_eff

k_eff1.001000

ρ9.99001e-4

pcm99.90

Σ = N · σ (N in atoms/barn-cm, σ in barn → Σ in cm⁻¹). Mean free path λ = 1/Σ.

N (atoms/barn-cm)

σ (barn)

Σ (cm⁻¹)2.20625e-2

λ (cm)45.326