Prepare Solution Calculator
Use the two tools below to quickly calculate either (1) how much solid to weigh for a target molarity, or (2) how much stock solution to use for a dilution.
Solid Solute → Target Molarity
Formula: grams = (C × V × MW) / purity
Stock Dilution (C₁V₁ = C₂V₂)
Find stock volume and diluent needed for your final concentration.
How to Use This Prepare Solution Calculator
Preparing lab solutions accurately matters. Whether you are making a buffer for biochemistry, a standard for analytical chemistry, or a reagent for cell culture, small concentration mistakes can create large experimental errors. This calculator helps you avoid manual math errors and keeps your workflow consistent.
When to use the “Solid Solute” tool
- You are starting from a dry powder.
- You know the molecular weight of your compound.
- You have a target molar concentration and final volume.
- You need purity correction (for example, 98% pure reagent).
When to use the “Stock Dilution” tool
- You already have a concentrated stock solution.
- You want to make a weaker working solution.
- You know C1, C2, and V2, and need V1.
1) moles = concentration × volume
2) grams = moles × molecular weight
3) purity corrected grams = grams / (purity/100)
4) C₁V₁ = C₂V₂ for dilution calculations
Worked Example 1: Make 250 mL of 50 mM NaCl
Suppose you want 250 mL of 50 mM sodium chloride. NaCl molecular weight is 58.44 g/mol.
- Convert concentration: 50 mM = 0.05 M
- Convert volume: 250 mL = 0.25 L
- Moles needed = 0.05 × 0.25 = 0.0125 mol
- Mass needed = 0.0125 × 58.44 = 0.7305 g
If your NaCl were only 99% pure, divide by 0.99 and weigh approximately 0.738 g.
Worked Example 2: Dilute 1 M stock to 100 mM, final volume 100 mL
- C1 = 1 M
- C2 = 0.1 M
- V2 = 100 mL
- V1 = (C2 × V2) / C1 = (0.1 × 100 mL)/1 = 10 mL
So you would pipette 10 mL of stock and add diluent up to 100 mL total volume (about 90 mL diluent).
Best Practices for Accurate Solution Preparation
1) Use calibrated equipment
Use an analytical balance for mass and a volumetric flask for final volume whenever high precision is needed. Pipette accuracy matters, especially in the microliter range.
2) Always account for purity and form
Hydrated salts, technical-grade reagents, and moisture-sensitive compounds can all shift the true amount of active material. Use the correct molecular weight for the exact chemical form.
3) Dissolve first, then bring to volume
For most solutions, dissolve the solid in about 70–80% of the final volume, then bring up to the final mark. This gives better volumetric accuracy than adding full volume first.
4) Label everything clearly
Add concentration, solvent, pH (if relevant), date prepared, and initials. Good labeling prevents wasted time and costly mix-ups.
Common Mistakes to Avoid
- Mixing up mM and M (1000× error).
- Forgetting to convert mL to L in molarity equations.
- Assuming reagent purity is 100% when it is not.
- Using C₁V₁ = C₂V₂ when a chemical reaction changes concentration (not a simple dilution).
- Rounding too early during multi-step calculations.
Quick Unit Reference
- 1 L = 1000 mL = 1,000,000 µL
- 1 M = 1000 mM = 1,000,000 µM
- 1 g = 1000 mg = 1,000,000 µg
This calculator is designed to be fast and practical for day-to-day lab work. For regulated environments (GLP/GMP), always verify with your SOP and instrument calibration requirements.