Three lab essentials in one free calculator. Work out how many grams to weigh for a solution with the molarity calculator, solve any dilution with C₁V₁ = C₂V₂, and convert between pH, pOH, [H⁺] and [OH⁻], including weak acids from Ka. Built by a team that runs an ISO/IEC 17025 accredited testing lab.
Fill in three of the four boxes and leave the one you want blank.
Leave exactly one box blank. Use the same units on both sides.
Formulas
Worked examples
- Making a solution: 250 mL of 0.5 M NaCl needs 0.5 × 0.250 × 58.44 = 7.31 g NaCl, dissolved and made up to the 250 mL mark in a volumetric flask.
- Diluting a stock: to make 500 mL of 1 M HCl from 12 M concentrated acid, V₁ = 1 × 500 ÷ 12 = 41.7 mL of stock, made up to 500 mL (add acid to water, never water to acid).
- pH: 0.01 M HCl is a strong acid, so [H⁺] = 0.01 and pH = 2. A 0.1 M acetic acid solution (Ka 1.8 × 10⁻⁵) has pH ≈ 2.88.
Good lab practice
Use volumetric glassware, weigh on a calibrated balance, and correct for purity if your reagent isn’t 100% (divide the mass by the assay fraction, e.g. ÷ 0.995). pH values from this calculator assume 25 °C, complete dissociation for strong acids and bases, and ideal (dilute) solutions.
Frequently asked questions
How do I calculate molarity?
Divide moles of solute by litres of solution. If you know the mass, first convert it to moles using the molar mass. Fill in any three of formula/molar mass, mass, volume and concentration and the calculator finds the fourth.
How many grams do I need to make a solution?
Multiply molarity × volume in litres × molar mass. For 1 L of 0.1 M NaOH: 0.1 × 1 × 40.00 = 4.00 g.
How do I use C1V1 = C2V2?
Leave the unknown blank and fill in the other three in matching units. The calculator gives the missing value and how much solvent to add to reach the final volume.
How do I calculate pH from concentration?
For a strong acid, pH = −log[H⁺], so 0.001 M HCl has pH 3. For a strong base, find pOH = −log[OH⁻], then pH = 14 − pOH. For weak acids, choose the weak acid option and enter Ka.
Can I type a formula instead of a molar mass?
Yes. Type a formula such as CuSO4·5H2O and the calculator works out the molar mass for you, or type a number like 58.44 directly.
Related tools
Free educational tool by HawkInc. Results are calculated in your browser and rounded for display; check critical work by hand or with a second method.