PBS and Buffer Recipes, with a Buffer Calculator
Phosphate-buffered saline (PBS), citrate and acetate buffers are among the most widely used solutions in the lab. This page gives the standard recipes with a calculator that scales them to any batch size, plus an acetate buffer calculator for any pH between 3.8 and 5.8.
Buffer recipe calculator
Recipe scaler
Choose a buffer and batch volume. Amounts update as you type.
1× PBS, pH 7.4
This is the standard formulation (as published in Cold Spring Harbor Protocols): 137 mM NaCl, 2.7 mM KCl, 10 mM Na₂HPO₄ and 1.8 mM KH₂PO₄.
| Component | Per litre | Final concentration |
|---|---|---|
| Sodium chloride (NaCl) | 8.00 g | 137 mM |
| Potassium chloride (KCl) | 0.20 g | 2.7 mM |
| Disodium hydrogen phosphate, anhydrous (Na₂HPO₄) | 1.44 g | 10 mM |
| Potassium dihydrogen phosphate (KH₂PO₄) | 0.24 g | 1.8 mM |
- Dissolve the salts in about 800 mL of purified water.
- Adjust to pH 7.4 with HCl or NaOH.
- Make up to 1 L.
- Sterilise by autoclaving (121 °C, 20 minutes) or by filtering through a 0.22 µm filter. Store at room temperature.
Using the heptahydrate form (Na₂HPO₄·7H₂O)? Use 2.68 g per litre instead of 1.44 g. The calculator does this for you. Some protocols use calcium- and magnesium-free PBS for cell work; this recipe contains neither.
10× PBS stock
Ten times every amount above makes a concentrated stock that saves shelf space; dilute 1 part with 9 parts of purified water before use. A 10× stock reads below pH 7.4 because of the higher concentration, so check and adjust the pH after diluting to 1×. If crystals form in a cold room, warm the bottle and mix until they redissolve.
Short on time? Ready-made 1× isotonic PBS, pH 7.4 is available in 100 mL bottles.
10 mM sodium citrate buffer, pH 6.0
Dissolve 2.94 g of trisodium citrate dihydrate (MW 294.10 g/mol) in about 800 mL of purified water, adjust to pH 6.0 with 1 M HCl and make up to 1 L. Store at room temperature, or at 2–8 °C for longer keeping. Some protocols add 0.05% Tween 20 after pH adjustment. A ready-made 1× sodium citrate buffer, pH 6.0 is available in 500 mL bottles.
Acetate buffer calculator (pH 3.8 to 5.8)
Acetate buffer
Uses the Henderson–Hasselbalch equation with pKa 4.76 at 25 °C. Always confirm the final pH with a calibrated meter.
How it works: pH = pKa + log([acetate] ÷ [acetic acid]). The calculator finds the ratio for your target pH, splits the total concentration between sodium acetate and acetic acid, and converts the acid to a volume of glacial acetic acid (60.05 g/mol, density 1.049 g/mL). Buffers work best within about one pH unit of the pKa, which is why the range is limited to pH 3.8–5.8. Temperature and ionic strength shift the real pKa slightly, so the measured pH may differ by a few hundredths.
Tips for consistent buffers
- Calibrate the pH meter with at least two standards that bracket your target pH, at the temperature you will use the buffer.
- Make up with purified water such as WFI water to avoid ions that shift pH or interfere with assays.
- Label every bottle with the buffer, concentration, pH, date and initials.
- Aliquot into sterile vials to avoid contaminating the whole batch; see our aliquoting guide.
Related: dilution and molarity calculator · syringe filter selection guide.
Recipes and calculators are provided as a convenience; follow your own validated protocols where they differ. Union Biolabs products are supplied for laboratory research use only.