Chemistry Calculators

Find the molar mass of any compound from its chemical formula, with a per-element mass breakdown.

Convert between moles and grams using molar mass, and see the number of molecules involved.

Use C₁V₁ = C₂V₂ to find how much stock solution to dilute to reach a target concentration and volume.

Calculate the percent yield of a reaction from the actual and theoretical yields.

Find the theoretical yield of a product from the moles of limiting reactant, mole ratio and molar mass.

Find the mass percent of every element in a compound from its chemical formula.

Turn element mass percentages or grams into the simplest whole-number (empirical) formula.

Solve the combined gas law P₁V₁/T₁ = P₂V₂/T₂ for the new volume of a gas.

Use Gay-Lussac's law to find the new pressure of a gas when its temperature changes at constant volume.

Work out parts per million from a mass of solute in a solution, convert between ppm, ppb, percent, mg/L, µg/L, g/L, grains per gallon and molarity with a density correction, or convert gas ppm to mg/m³ at any temperature and pressure.

Calculate how much a solute raises the boiling point of a solvent using ΔTb = i·Kb·m.

Calculate how much a solute lowers the freezing point of a solvent using ΔTf = i·Kf·m.

Find the molarity of a solution from the mass of solute, its molar mass and the solution volume.

Convert between a number of atoms or molecules and moles using Avogadro's number.

Calculate a reaction rate constant from the Arrhenius equation using activation energy and temperature.

Find the molarity of a solution directly from the moles of solute and the solution volume in litres.

Work out how much stock solution and solvent you need to reach a target concentration using C₁V₁ = C₂V₂.

Measure the efficiency of a reaction as percent yield from the actual and theoretical product masses.

Find the mass percent (percent by weight) of a component from the solute and solvent masses.

Convert a mass in grams to moles using molar mass, and see how many molecules that is.

Solve PV = nRT for the number of moles of a gas from its pressure, volume and temperature.

Calculate the pH of a strong acid or base solution from its molar concentration.

Find the pOH and pH of a solution from its hydroxide-ion concentration, or convert between pH and pOH.

Calculate the molecular weight (molar mass) of a compound from its chemical formula.

Calculate mass/volume percent concentration (% m/v) from grams of solute and millilitres of solution.

Use Boyle's law P₁V₁ = P₂V₂ to find a gas's new pressure or volume at constant temperature.

Use Charles's law V₁/T₁ = V₂/T₂ to find a gas's new volume when its temperature changes at constant pressure.

Work out molality (mol solute per kg solvent) from the mass of solute, its molar mass and the mass of solvent.

Find the mole fraction and mole percent of each component in a mixture of 2 to 4 substances from moles or from grams and molar mass, with mass percent, molality, partial pressures (Dalton’s law) and the worked steps.

Find normality from molarity, from grams and volume, or from a concentrated acid’s % w/w and density; work out the grams to weigh or the stock volume to dilute for a target normality, or the unknown normality from a titration (N₁V₁ = N₂V₂). With common acids, bases and redox reagents, equivalent weight, meq/L and the steps.

Calculate concentration in parts per million from the mass of solute and the mass of the whole solution.

Find the theoretical yield in grams from the moles of limiting reagent, the mole ratio and the product molar mass.

Compare two reactants and their coefficients to find which one is the limiting reagent and which is in excess.

Find the density of an ideal gas from its pressure, molar mass and temperature using ρ = PM/RT.

Solve the combined gas law P₁V₁/T₁ = P₂V₂/T₂ for the final pressure P₂ after a volume and temperature change.

Find the pH of a buffer from its pKa and the concentrations of the conjugate base and weak acid.

Find how much of a radioactive sample remains after a given time from its half-life, plus the decay constant.

Find the activation energy from two rate constants measured at two temperatures using the two-point Arrhenius equation.

Calculate the heat absorbed or released with q = m·c·ΔT, and the molar enthalpy change of a reaction.

Convert an amount in moles to a mass in grams using the substance’s molar mass — the everyday bench conversion for weighing out a reaction.

Turn moles (or grams) into the number of molecules and atoms with Avogadro’s number, or count particles back to moles. Type a formula such as H2O or Ca(OH)2 to get atoms per molecule, the atoms of each element, the molar mass and the worked steps.

Find the empirical formula of a compound from the mass percentages of carbon, hydrogen and oxygen — the classic combustion-analysis calculation.

Calculate the percentage purity of a sample from the mass of pure substance it contains and its total mass.

Work out how much concentrated stock and how much water to combine to reach a target concentration in parts per million.

Calculate how far a dissolved solute lowers a solvent’s freezing point from its molality, cryoscopic constant and van’t Hoff factor.

Find how much a dissolved solute raises a solvent’s boiling point from its molality, ebullioscopic constant and van’t Hoff factor.

Compute the osmotic pressure of a solution from its molarity, temperature and van’t Hoff factor using the van’t Hoff equation.

Calculate the equilibrium constant Kc for a reaction aA + bB ⇌ cC + dD from equilibrium concentrations and stoichiometric coefficients.

Find the average rate of a chemical reaction from the change in concentration over a time interval, adjusted for stoichiometry.

Convert energy between electronvolts (meV to TeV), joules and kJ or kcal per mole using the exact SI value of the elementary charge — plus the photon wavelength, frequency, wavenumber, temperature and mass equivalents, a full table of units and typical energies to compare with.

Calculate the energy and frequency of a photon from its wavelength using E = hc/λ — for light, spectroscopy and quantum problems.

Find the pH of a buffer directly from its base-to-acid ratio and the acid’s pKa using the Henderson–Hasselbalch equation.

Convert between an acid dissociation constant Ka and its pKa in either direction — the logarithmic relationship at the heart of acid strength.

Calculate the pH of a weak monoprotic acid from its Ka and concentration, solved exactly with the equilibrium quadratic — no simplifying assumption.

Find what fraction of a weak acid is ionized at equilibrium from its Ka and concentration — the degree of dissociation as a percentage.

Find the volume of titrant needed to reach the equivalence point of an acid–base titration from the analyte’s concentration, volume and mole ratio.

Compute the solubility product Ksp of a sparingly soluble salt from its molar solubility and its dissolution stoichiometry.

See how much a 1:1 salt’s solubility drops when a common ion is already present, solved from its Ksp and the common-ion concentration.

Find the actual cell potential under non-standard conditions from the standard potential, electrons transferred, reaction quotient and temperature.

Find the oxidation number of a target element in a species from the standard rules for hydrogen (+1), oxygen (−2) and the overall charge.

Work out how many grams of solute to weigh out to make a solution of a target molarity and volume from the compound’s molar mass.

Convert between moles of a substance and the volume of gas it produces or consumes at STP using the molar volume and a balanced mole ratio.

Find the equilibrium temperature when two substances at different temperatures are mixed, from their masses, specific heats and starting temperatures.

Find the degree of unsaturation (index of hydrogen deficiency) of a molecular formula to reveal how many rings and π bonds it contains.

Calculate the molar absorptivity (extinction coefficient) of a species from its absorbance, concentration and path length using the Beer–Lambert law.

Find the concentration at every stage of a serial dilution from the stock concentration, the fold-dilution per step and the number of steps.

Work out how many grams of weak acid and conjugate base to weigh out to prepare a buffer at a target pH, total concentration and volume.

Convert specific gravity to density in g/cm³, kg/m³, lb/ft³ and lb/gal, or density back to specific gravity, against water at 4, 15, 20 or 25 °C, 60 °F, any temperature from 0 to 40 °C, air or a custom reference. Also gives API gravity, Baumé degrees, specific volume and the weight of a volume.

Convert a % w/w (weight/weight) concentration into molarity from the solution density and the solute’s molar mass — the usual step for concentrated reagents.

Measure how efficiently a reaction converts reactant mass into the desired product — the percentage atom economy, a key green-chemistry metric.

Compare the mass you actually recovered against the theoretical maximum to get the percent yield of a reaction, plus the mass lost.

Identify which of two reactants runs out first from their masses, molar masses and balanced coefficients — and how much of the excess is left over.

Calculate the density of an ideal gas at any pressure and temperature from its molar mass using the ideal gas law rearranged for density.

Predict the vapor pressure of a liquid at a new temperature from a known vapor pressure, the two temperatures and the enthalpy of vaporization.

Determine an unknown solute’s molar mass from freezing-point depression — the classic colligative method — using the solvent’s cryoscopic constant.

Work out exactly how much chlorine product to add to raise your pool from its current free-chlorine level to a target ppm.

Find how much marine salt to add to reach a target salinity in a saltwater or brackish aquarium of any volume.

Convert water hardness between ppm (mg/L as CaCO₃), grains per gallon, German, French and English degrees, mmol/L and meq/L, see its class on the USGS, WQA or German scale, and get the softener hardness setting with an iron allowance.

Convert total dissolved solids (ppm) to electrical conductivity in µS/cm and mS/cm using a selectable conversion factor.

Calculate the sodium bicarbonate (baking soda) needed to raise pool or spa total alkalinity to your target in ppm.

Dilute a concentrated acid safely: find how much stock acid and how much water make a target molarity — always adding acid to water.

Convert a molar concentration (mol/L) to weight/volume and weight/weight percent using the solute molar mass and solution density.

Compute the Langelier Saturation Index (LSI) from pH, temperature, TDS, calcium hardness and alkalinity to see if water scales or corrodes.

Gauge how efficiently a reaction turns reactant into product: grams of product per gram of reactant, plus percent yield.

From a calorimetry experiment, find the molar enthalpy of combustion of a fuel using water mass, temperature rise and fuel burned.

Estimate a reaction’s enthalpy change from bond energies: energy to break reactant bonds minus energy released forming product bonds.

Check that the oxidation states in a formula add up to the species’ overall charge — a quick validity test for up to three elements.

Convert a mass in grams to a volume in milliliters using the substance density — the correct way, since grams and millilitres only match for water.

Convert a solution’s mass percent (w/w) into molality (mol solute per kg solvent) from the solute’s molar mass — no solution density needed.

Convert a concentration in parts per million to molarity (mol/L) using the solute molar mass and the solution density.

Convert a mass in milligrams to milliequivalents using the molar mass and valence — the unit used for electrolytes in clinical and lab work.

Find the percentage of water of crystallization in a hydrate ·nH₂O from its formula, work out n and the hydrate formula from lab masses before and after heating (with or without the crucible), or find n from a percent water. Common hydrates built in, with percent error, expected mass loss and a % water table for n = 0 to 12.

Find how many empirical units make up the molecular formula by dividing the molecular molar mass by the empirical formula mass.

Compute the weighted average atomic mass of an element from two isotopes’ masses and their percent abundances.

Find the formal charge on an atom in a Lewis structure from its valence electrons, lone-pair electrons and number of bonds.

Add bonded atoms and lone pairs to get the steric number and the VSEPR electron-domain geometry of a central atom.

Compute molecular-orbital bond order from the number of bonding and antibonding electrons — and see whether the species is stable or paramagnetic-friendly.

Find the reaction order in a reactant from two experiments — the initial concentration and initial rate for each.

Find the activation energy from two rate constants measured at two temperatures using the two-point Arrhenius equation.

Convert a pH value into the hydrogen ion concentration [H⁺] in mol/L, with matching pOH and [OH⁻].

Convert a pOH value into the hydroxide ion concentration [OH⁻] in mol/L, with matching pH and [H⁺].

Estimate the buffer capacity of a weak-acid/conjugate-base buffer from the acid and base concentrations.

Find the volume of base needed to neutralize an acid from their concentrations and proton counts.

Calculate the molar heat (enthalpy) of solution from a calorimetry temperature change and moles of solute.

Find the equilibrium temperature when two substances at different temperatures are mixed, using mass and specific heat.

Estimate the energy and calories released when a fuel burns, from its mass and heat of combustion.

Calculate the density of a two-component gas mixture from its composition, pressure and temperature.

Find each gas's partial pressure in a mixture from its moles and the total pressure, using Dalton's law.

Use the coefficients from a balanced equation to convert moles of one substance into moles of another.

Find the percent water in a hydrate from the mass before and after heating, plus the number of water molecules.

Calculate how much stock solution and diluent to combine to make a working solution at the concentration and volume you need.

Solve C1V1 = C2V2 for the stock volume, final concentration, final volume or stock concentration — with M to pM and L to µL unit menus, the solvent to add, dilution factor and ratio, moles and grams of solute, a prep table and the worked steps.

Convert between pH, pOH, and hydrogen and hydroxide ion concentrations at 25°C.

ΔG from ΔH, ΔS and temperature — spontaneity, the crossover temperature where ΔG = 0, the equilibrium constant K, and ΔG under non-standard conditions from the reaction quotient.

Reaction enthalpy from standard enthalpies of formation — enter ΔHf° and coefficients for reactants and products, get ΔH°rxn, per-species contributions and whether the reaction is exo- or endothermic.

Convert between the pressure and concentration equilibrium constants for a gas reaction — Kp = Kc(RT)^Δn — with Δn from the balanced equation and the constant in atm or bar.

Fraction of a weak electrolyte or gas that dissociates — from Ka and concentration (Ostwald’s law), from conductivity, or from the observed van’t Hoff factor / vapour density.

How an equilibrium constant changes with temperature — K at a new temperature from ΔH°, or ΔH° from two K values — with ΔS° and the direction Le Chatelier predicts.

Vapour pressure of an ideal two-component solution — partial pressures, total pressure, vapour-phase composition and relative volatility from mole fractions and pure-component vapour pressures.

Mass of metal deposited or gas evolved from current and time — or the time and charge needed for a target mass — for any ion with its molar mass and charge, with efficiency and gas volume at STP.

E°cell from two half-cell reduction potentials — which electrode is the cathode, the cell notation, ΔG° and the equilibrium constant — with a table of common couples.

pH of a salt from a weak acid or weak base by hydrolysis — Kb of the conjugate base or Ka of the conjugate acid from the parent constant, degree of hydrolysis, and the weak-acid/weak-base case.

Ionic character of a bond from the electronegativity difference (Pauling’s equation) or from the measured dipole moment and bond length — with the bond type and the Hannay–Smyth estimate.

Relative rates of effusion or diffusion of two gases from their molar masses, the time ratio, the molar mass of an unknown gas from measured rates, and rms speeds at a given temperature.

Half-life and remaining concentration for zero-, first- and second-order reactions from the rate constant and initial concentration — with time to any percentage conversion and how t½ changes with concentration.

Equilibrium concentrations for A ⇌ B + C (or A ⇌ 2B, A + B ⇌ C…) from K and initial concentrations — the ICE table filled in, the exact quadratic solution, extent of reaction and a check of the 5% approximation.

Estimate the lattice energy of an ionic compound from ion charges, ionic radii and the number of ions per formula unit using the Kapustinskii equation — with a Born–Landé comparison for common structures.

Total, calcium and magnesium hardness from Ca²⁺ and Mg²⁺ (mg/L, mmol/L or as CaCO₃), from an EDTA titration or from a total you already have — in mg/L as CaCO₃, ppm, gpg, °dH, °fH, °e, mmol/L and meq/L, with the hardness class on US, WQA and German scales, temporary vs permanent hardness and water-softener sizing.

Convert centrifuge RPM to relative centrifugal force (× g) and back for any rotor radius (cm, mm or inches), adjust run time when your rotor spins slower, and get the k-factor, pelleting time, g at r-min, a g-vs-speed chart and the worked steps.

Solve the Beer–Lambert law A = ε·l·c for concentration, absorbance, molar extinction coefficient or path length, with unit menus (nM–M, mm–m, M⁻¹ or mM⁻¹ cm⁻¹). Enter absorbance, percent transmittance or I and I₀, subtract a blank, correct for dilution, get mass concentration and a linear-range check.

Balance any chemical equation — combustion, redox, ionic (with charges) or hydrates — by the matrix method and get the smallest whole-number coefficients with an atom-by-atom check of both sides.

Use Henry's law, C = kH × P, to find how much oxygen, nitrogen, CO₂ or another gas dissolves in water at a given partial pressure and temperature — in mol/L, mmol/L and mg/L.

Solve the van der Waals equation for the pressure of a real gas (CO₂, N₂, O₂, H₂O, NH₃…) and compare it with the ideal gas law — compressibility factor Z, attraction and repulsion terms and critical constants.

Find the pH at any point of an acid–base titration — strong or weak acid with a strong base, or strong or weak base with a strong acid — with the equivalence volume, equivalence and half-equivalence pH and a full curve table.

Find the root-mean-square speed of gas molecules, v_rms = √(3RT/M), plus the mean and most probable Maxwell–Boltzmann speeds and the average kinetic energy, for any gas and temperature.

Calculate the effective nuclear charge (Z_eff) felt by any electron with Slater's rules — shielding constant, electron configuration and a group-by-group shielding table for elements 1 to 86.

Calculate the ionic strength of a solution, I = ½ Σ cᵢzᵢ², from up to four ions, with a charge-balance check, Davies activity coefficients at 25 °C and the Debye length.

Calculate enantiomeric excess (ee) and the enantiomer ratio from an observed optical rotation and the specific rotation of the pure enantiomer, or from the amounts or HPLC peak areas of each enantiomer.

Find how many grams or millilitres of solute you need to make a percent solution — % w/v (g/100 mL), % v/v (mL/100 mL) or % w/w (g/100 g) — for any final volume or mass.

Calculate the osmolarity (mOsm/L) of a solution such as normal saline, D5W or potassium chloride from its % w/v, mg/mL, g/L or mmol/L, molar mass and number of dissolved particles.

Calculate mass accuracy in ppm and mDa between a measured and a theoretical m/z for high-resolution mass spectrometry, plus the ± Da window for a ppm tolerance and a pass/fail check.

Solve Avogadro’s law V₁/n₁ = V₂/n₂ for the final volume or the final amount of gas in moles at constant temperature and pressure, with the molar volume and the change in volume and moles.

Calculate the pH, pOH, hydroxide concentration and percent ionization of a weak base such as ammonia from Kb and concentration, solved exactly (including water) and compared with the √(Kb·C) shortcut.

Polarimetry calculator: specific rotation [α] = α/(l·c) from the observed rotation, tube length and concentration — or solve for the observed rotation or the concentration of a chiral compound such as sucrose.