The diffusion calculator — plus the laws of chemistry & physics
Solve Fick's laws, diffusion coefficients, gas laws, kinetics, electrochemistry and mechanics in seconds. Every calculator includes unit conversion, step-by-step working and a clear explanation of the law behind it.
What is diffusion?
Diffusion is the net movement of particles from a region of higher concentration to one of lower concentration, driven by their random thermal motion. It is how oxygen reaches your cells, how dopants enter silicon chips, how carbon hardens steel, how perfume fills a room and how drugs cross membranes.
The rate of diffusion is described by Fick's first law, J = −D·dC/dx. The flux J is proportional to the concentration gradient, and the diffusion coefficient D sets the speed. Fick's second law describes how concentration profiles change over time, and the diffusion length √(2nDt) tells you how far particles travel.
Try the live calculator, then explore the full set of diffusion calculators.
Diffusion calculators
Mass transport, from Fick's laws to Brownian motion.
Fick's First Law Calculator
Diffusion flux from a concentration gradient
Fick's Second Law Calculator
Concentration vs. depth and time (erf solution)
Diffusion Coefficient vs Temperature (Arrhenius)
D = D₀·exp(−Q/RT) for solids
Stokes–Einstein Equation Calculator
Diffusion coefficient of a particle in a fluid
Diffusion Length & Time Calculator
Mean displacement L = √(2nDt)
Graham's Law of Effusion Calculator
Relative effusion/diffusion rates of gases
Membrane Diffusion & Permeability Calculator
Flux through a membrane with partition coefficient
Einstein Relation Calculator (Mobility ↔ Diffusivity)
D = μ·k_B·T / q for charge carriers and ions
Thermal Diffusivity Calculator
α = k / (ρ·cₚ) — how fast heat diffuses
Popular chemistry & physics tools
The equations students and scientists reach for every day.
Ideal Gas Law Calculator
PV = nRT
Molarity Calculator
Concentration from mass, molar mass and volume
Dilution Calculator (C₁V₁ = C₂V₂)
Stock solution dilution
pH Calculator
pH, pOH, [H⁺] and [OH⁻] at 25 °C
Half-Life & Radioactive Decay Calculator
N = N₀·(½)^(t/t½)
Arrhenius Equation Calculator
Reaction rate constant vs temperature
Ohm's Law Calculator
V = I·R and electrical power
Fourier's Law of Heat Conduction Calculator
Heat transfer rate through a wall
Laws library
Every law explained in one place — statements, formulas, history and links to calculators.
Why use DiffusionCalculator.com?
- Solve for any variable. Each calculator rearranges its equation for whichever quantity you need.
- Automatic unit conversion. Mix cm²/s with µm, °C with kPa, mmol/L with hours. Everything is converted to SI internally.
- Show your work. Step-by-step working shows the formula, the SI values used and the result.
- Shareable results. Copy a link that reopens the calculator with your exact inputs.
- Fast and private. Calculations run in your browser. Nothing you type is sent to a server.