Introduction
A buffer is a solution that keeps its pH steady. Even when you add a little acid or base, the pH barely moves. Labs use buffers every day for cell work, protein tests, DNA gels, and more.
This buffer calculator tells you exactly how much of each chemical to weigh out. Pick your buffer, type in the volume, the concentration, and the pH you want. The tool then gives you the mass of every component in grams, milligrams, or other units you choose.
You can pick from more than 30 buffer systems, such as HEPES, Tris-HCl, PBS, phosphate, citrate, acetate, MES, MOPS, and TAE. Each one shows its pKa and its useful pH range, so you can see at a glance if it fits your target pH.
The calculator also does the harder chemistry for you. It corrects the pKa for temperature, adjusts for ionic strength using the Debye-Hückel equation, and works out how much salt to add to hit a set ionic strength. It shows your buffer capacity, warns you if your pH is too far from the pKa, and predicts how the pH will shift when you move the buffer from the bench to a warm incubator or a cold room.
Along with the numbers, you get a step-by-step recipe, the full math behind each answer, and charts of buffer capacity and component mass. Everything updates as soon as you change an input. If you only need a single pH figure for a strong or weak acid, our pH Calculator and Acid Base Calculator handle that in one step.
How to use our Buffer Calculator
Pick your buffer, type in your volume, strength, and target pH, and the calculator tells you how much of each chemical to weigh out. You also get the buffer capacity, the ionic strength, a step-by-step recipe, and the full math behind it.
Filter by category: Click a category chip, like Good's Biological or Phosphate-Based, to shorten the buffer list. Click "Show All" to see every buffer again.
Select Buffer: Choose the buffer system you want to make. Each choice shows its pKa and its useful pH range, so pick one with a pKa close to your target pH.
Display masses in: Pick the unit for your results, such as grams, milligrams, micrograms, kilograms, ounces, or pounds. To move between metric and imperial weights by hand, see the Grams to Ounces Calculator or the Ounces to Grams Calculator.
Final Volume: Enter how much buffer you need and pick the unit (µL, mL, L, fl oz, or gal). You can also tap a preset button like 500 mL or 1000 mL. Changing the unit converts your number for you. For odd container sizes, the Volume Conversion Calculator and Tank Volume Calculator can help.
Buffer Concentration: Type the strength you want and choose nM, µM, mM, or M. This box only shows for buffers where you set the concentration yourself. If you are working from a molar recipe, the Molarity Calculator and Mole Calculator cover the underlying moles-per-litre math.
Concentration Multiple (×): For stock recipes like TAE, TE, or TBST, enter how strong you want the stock, such as 1×, 10×, or 50×. To dilute that stock down to a working strength, use the Dilution Calculator or the Serial Dilution Calculator.
Target pH: Enter the pH you want. Some buffers give you a drop-down list of tested pH values instead, and a few, like TBST, have a fixed pH you cannot change. The colour bar shows if your pH sits in the buffer's best range.
Adjust Ionic Strength: Tick this box if you want to add salt to hit a set ionic strength. Untick it to skip the salt.
Target Ionic Strength (mM): Enter the total ionic strength you need. 154 mM matches normal saline. For related solution measures, see the Osmolality Calculator and the PPM Calculator.
Adjustment Salt: Pick NaCl, KCl, or Na₂SO₄ to make up the ionic strength. Choose "Other salt" to type your own molar mass and charge type. The Molecular Weight Calculator gives you the molar mass of any formula you enter.
Preparation Temperature: Enter the temperature of the room where you mix and pH the buffer. Choose °C, °F, or K. The Celsius to Fahrenheit Calculator and Fahrenheit to Celsius Calculator are handy if your thermometer reads in the other scale.
Use Temperature: Enter the temperature where the buffer will be used. The tool shows how much the pH will drift between the two temperatures.
Form / Hydration: In the results table, some chemicals let you switch between anhydrous and hydrated forms. Pick the one on your shelf and the mass updates.
Calculate and Reset: Results update as you type, but you can press Calculate any time. Press Reset to Defaults to start over. When you report your masses, the Sig Fig Calculator helps you round to the right number of significant figures.
What Is a Buffer Solution?
A buffer is a water solution that keeps its pH almost the same, even when you add a little acid or base. It works because it holds two partners: a weak acid and its matching base (called the conjugate base). The acid part soaks up extra base. The base part soaks up extra acid. This keeps the pH steady.
Buffers matter because most living things and many lab tests only work in a narrow pH window. Blood, cells, enzymes, DNA gels, and medicines all need a stable pH. That is why buffers are used every day in biology, chemistry, food science, and medicine.
pKa and Buffer Range
Each weak acid has a number called the pKa. At that pH, half the buffer is acid and half is base. This is the strongest point of the buffer. As a rule, a buffer works well from about one pH unit below to one pH unit above its pKa. Outside that range, it gets weak and cannot hold the pH.
So pick a buffer whose pKa is close to the pH you want. For pH 7.4 work, HEPES (pKa 7.48) or phosphate (pKa 7.20) are good picks. For pH 4.8, acetate (pKa 4.76) fits better.
The Henderson–Hasselbalch Equation
This simple formula links pH, pKa, and the mix of acid and base:
pH = pKa + log ( [base] / [acid] )
If you know the pH you want and the pKa of your buffer, you can solve for how much acid form and how much base form you need. Then you multiply by the volume and the molar mass to get the grams to weigh out. The log term is a base-10 logarithm, and our Log Calculator or Antilog Calculator can check that step by hand.
Buffer Capacity (β)
Buffer capacity tells you how much acid or base the buffer can take before the pH moves. It is written as β, in moles per liter per pH unit. Two things raise it:
- Higher concentration — more buffer means more capacity.
- pH close to the pKa — capacity is highest right at the pKa and drops fast as you move away.
Why Temperature Changes pH
The pKa of a buffer shifts when the temperature changes. Each buffer has its own rate, called dpKa/dT. Tris is a big one: about −0.028 pH units per °C. So a Tris buffer set to pH 8.00 in a cold room at 4 °C will read near pH 7.10 at 37 °C. Phosphate barely moves at all. Always note the temperature you set the pH at, and check it again at the temperature you will use it. The Temperature Calculator converts between scales if your notes mix °C and °F.
Ionic Strength and Salt
Ionic strength is a measure of how many charged ions are in the solution. Ions crowd around the buffer molecules and change how they act, which shifts the real pKa a little. Many recipes add a neutral salt such as NaCl or KCl to set the ionic strength to a set value. For cell and protein work, people often aim for about 150 mM, close to the level inside the body.
Common Buffer Families
| Family | Examples | Useful pH |
|---|---|---|
| Good's biological buffers | MES, PIPES, MOPS, HEPES, Tricine, CHES, CAPS | 5.5 – 11 |
| Phosphate | Sodium phosphate, KH₂PO₄–NaOH, PBS | 5.8 – 8.0 |
| Citrate | Citric acid–sodium citrate, McIlvaine | 2.2 – 6.6 |
| Carbonate and borate | Borax, bicarbonate–carbonate | 7.4 – 10.8 |
| Amino acid | Glycine–HCl, Glycine–NaOH | 2.0 – 10.6 |
| Molecular biology stocks | TE, TAE, TBST, TEN | 7.4 – 8.0 |
Hydrates Matter When You Weigh
Many buffer salts come with water locked in the crystal. Sodium phosphate dibasic can be anhydrous (142 g/mol) or dodecahydrate (358 g/mol). The same number of moles needs a very different mass. Always check the label on your bottle and use the matching molar mass, or your buffer will be the wrong strength. If you need to scale a reaction that uses your buffer salts, the Stoichiometry Calculator works out the mole ratios.
Tips for Good Buffers
- Dissolve the solids in about 80% of the final water first, then set the pH, then top up to volume. Adding water last keeps the concentration right.
- Calibrate your pH meter at the same temperature you are working at.
- Pick a buffer that does not bind metals or react with your sample. Phosphate, for example, forms solids with calcium and magnesium.
- Store buffers cold and covered. Tris and phosphate can grow mold or bacteria over time.
- Carbonate buffers pick up CO₂ from the air, so keep them closed.
- Check your weighed masses against the target with the Percent Error Calculator when accuracy is critical.