A standard laboratory burette holds 50 mL, and that size dominates chemistry benches from introductory teaching labs to professional analytical settings. But burettes are manufactured in a range of capacities, from slim 5 mL microburettes up to 100 mL models, each suited to a different kind of work. The choice of size affects not just how much liquid you can dispense but how precisely you can measure what comes out, which is the entire point of using a burette in the first place.
Standard Sizes and What Each Is For
If you walk into a chemistry stockroom and ask for a burette without specifying, you will almost certainly be handed a 50 mL glass burette with 0.1 mL graduation marks. It is the default because it handles the widest range of routine titrations: you can dispense anywhere from a fraction of a milliliter to nearly the full 50 mL, and the 0.1 mL divisions let you estimate volumes to about 0.02 mL by reading between the lines. For everyday acid-base, redox, and complexometric titrations, that is more than enough precision.
A 25 mL burette is the next most common. Its graduations are typically the same 0.1 mL spacing, though some models use 0.05 mL divisions. The smaller total volume means each division represents a larger fraction of the whole delivery, which can slightly improve relative precision when you are titrating samples that only need 10 to 20 mL of titrant. It is a popular choice in pharmaceutical quality-control labs where sample sizes are modest and precision matters more than capacity.
At the smaller end, 10 mL and 5 mL microburettes serve situations where every drop counts. These are marked in 0.02 mL or 0.05 mL increments and are used in microanalysis, where the total volume delivered might be just a few milliliters. The finer graduations let you read volumes to roughly 0.01 mL. Microburettes show up in specialized titrations such as non-aqueous acid-base work with expensive solvents, or trace-level determinations where the sample size is tiny.
On the opposite end, 100 mL burettes exist for situations where you need to deliver large volumes with reasonable accuracy. These are less common in analytical chemistry and more likely to appear in industrial or environmental testing where titrant consumption per sample is high. The graduation marks are usually 0.2 mL apart, so the absolute reading precision is coarser than a 50 mL burette, and the instrument is physically unwieldy.
Why 50 mL Became the Standard
The 50 mL burette is a practical compromise. Most titrations in a general chemistry or analytical chemistry course consume somewhere between 15 and 45 mL of titrant, so 50 mL provides enough headroom that you rarely need to refill mid-titration. At the same time, 50 mL is small enough that the 0.1 mL divisions remain easy to read by eye. Scale the tube up to 100 mL and the markings spread farther apart physically, but each one represents a bigger jump in volume, which coarsens your measurement. Scale it down to 25 mL and you gain a bit of precision, but you run out of titrant more often, forcing refills that introduce their own small errors. The 50 mL size threads that needle well enough that it became the go-to for the majority of titration work worldwide.
Class A Versus Class B Tolerances
Not all burettes of the same size deliver the same accuracy. Glass burettes are manufactured to one of two tolerance classes defined by international standards. A Class A burette meets tighter specifications; a Class B burette is allowed roughly double the error. For a 50 mL Class A burette, the permitted tolerance is ±0.05 mL. A 25 mL Class A model allows ±0.03 mL, and a 10 mL Class A allows ±0.02 mL. Class B versions of each size double those numbers.
Those tolerances cover more than just manufacturing variation. Research on volumetric uncertainty has shown that the tolerance figure already accounts for the random error you introduce during normal use, so you do not need to add a separate allowance for user variability as long as you are working at room temperature and reading the meniscus correctly.1ScienceDirect / Talanta. Evaluation of measurement uncertainty in volumetric operations: the tolerance-based approach and the actual performance-based approach Temperature does matter, though: glass and liquid expand or contract with temperature changes, and working significantly above or below the calibration temperature (usually 20 °C) shifts the actual volume delivered. For most lab work at roughly room temperature, the shift is negligible, but in high-precision analytical work it becomes a factor worth correcting for.
Experimental studies evaluating volumetric glassware including graduated burettes have gone beyond manufacturer tolerances to measure the actual systematic and random errors introduced during routine use, using fill-and-weigh or fill-deliver-weigh methods with water.2Asian Journal of Research in Chemistry. A study and evaluation of Uncertainty in Volumetric Measurement The general finding is reassuring: a well-maintained Class A burette in competent hands performs close to its rated tolerance. The errors that push results outside tolerance tend to come from procedural mistakes rather than the glass itself.
Types of Burettes Beyond the Standard Glass Model
The classic straight-tube glass burette with a stopcock at the bottom is the one most people picture, but several other designs exist for specialized applications.
- Mohr burette: The simplest design, with a glass tube and a pinch clamp on a rubber tip instead of a glass or PTFE stopcock. It is inexpensive and common in teaching labs, but the rubber clip is less precise to control and can degrade when exposed to certain solvents.
- Geissler burette: Uses a glass stopcock ground to fit the barrel. More precise than a Mohr but requires greasing the stopcock and careful handling to avoid freezing the joint. Older labs still have drawers full of these.
- PTFE-stopcock burette: The modern standard for analytical work. The fluoropolymer stopcock does not need grease, resists most chemicals, and turns smoothly. Essentially all new Class A burettes sold today use this design.
- Bulb (piston) burette: A specialty instrument where fluid is stored in a glass bulb and delivered through a precision piston or plunger mechanism. Early research on high-precision titrimetry demonstrated that bulb burettes could achieve mechanical precision better than the best gravimetric (weight-based) techniques, reaching reproducibility on the order of about 1 part per million in carefully controlled experiments.3Canadian Journal of Chemistry. HIGH-PRECISION VOLUME TITRIMETRY That level of performance is far beyond what routine lab work requires, but it shows the ceiling of what volumetric delivery can achieve.
- Digital (electronic) burette: A motorized piston draws titrant from a bottle and dispenses it through a tip, with a digital display showing the volume delivered. These eliminate meniscus-reading errors entirely, can dispense in programmable increments, and are popular in quality-control labs where speed and consistency matter. Some are connected to automated titration systems controlled by software.4Analytica Chimica Acta. A microcomputer-controlled titrator for automated individual analysis
Digital burettes come in their own range of capacities, typically 10 mL, 25 mL, and 50 mL cartridges, with accuracy claims that rival or exceed Class A glass. They trade the ritual of reading a meniscus for the convenience of a readout, and they are especially useful when you need to perform dozens of titrations in a row without fatigue degrading your results.
What Burettes Are Actually Used For
The overwhelming primary use of a burette is titration: you add a reagent of known concentration to a sample until a chemical reaction is complete, then read the volume you dispensed. From that volume and the known concentration, you calculate how much of the target substance was in the sample. Titrations underpin a huge amount of real-world analysis, from checking the acid content of wine and fruit juice, to measuring calcium hardness in drinking water, to determining the active ingredient in pharmaceutical tablets.
Beyond classical titrations, burettes see use anywhere you need to deliver a precisely measured variable volume of liquid. Researchers preparing calibration standards sometimes use a burette to dispense exact aliquots of a stock solution into a series of flasks. Dispensing reagents for reaction kinetics studies is another application, where you need to add, say, exactly 3.75 mL of something and know you hit that number within a few hundredths of a milliliter.
Karl Fischer Titration
One specialized application worth knowing about is Karl Fischer titration, a method designed specifically to measure the water content of a sample. In the volumetric version, a burette delivers Karl Fischer reagent into a sealed cell containing the sample until all the water has reacted. The volume of reagent consumed tells you how much moisture was present.5The Canadian Journal of Chemical Engineering. Experimental methods in chemical engineering: Karl Fischer titration This technique is critical in industries where trace moisture matters: pharmaceuticals, petrochemicals, food production, and plastics manufacturing. Karl Fischer burettes are typically smaller capacity instruments, often 5 or 10 mL, because the reagent is expensive and the volumes involved are small.
Gas Burettes
A less well-known cousin is the gas burette, designed to measure volumes of gas rather than liquid. Gas burettes are sealed tubes filled with a confining liquid (often water or mercury, historically) that allows gas to be collected and its volume read from graduated markings. They were once essential for gas analysis in chemistry and appear occasionally in environmental or biological research measuring gas evolution from reactions or organisms. Their capacities vary widely, but 50 mL and 100 mL are common.
Common Mistakes That Affect Your Results
If you are getting inaccurate titration results, the burette itself is almost never the problem. The errors that plague real lab work are procedural, and they are consistent enough that instructors see the same ones year after year.
Air bubbles trapped in the burette tip or in the liquid column are one of the most frequently documented sources of error. A bubble sitting in the narrow section below the stopcock can dislodge during a titration, causing a sudden drop in the liquid level that looks like you dispensed more than you actually did. Studies tracking student technique in titration labs have specifically flagged air bubbles as a common procedural failure.6Royal Society of Chemistry. Enhancing formative and self-assessment with video playback to improve critique skills in a titration laboratory The fix is simple: before you start, open the stopcock fully and let liquid flush through the tip to chase out any trapped air. Tap the tip gently if needed.
Parallax error when reading the meniscus is another classic. The liquid in a burette forms a curved surface, and the volume is read at the bottom of that curve. If your eyes are above or below the meniscus, the graduation marks appear to shift, and your reading is off. The fix is to position your eyes level with the meniscus, which is easier said than done when the liquid level is near the top of a 50 mL burette and you are short.
Forgetting to rinse the burette with the titrant solution before filling is a subtler mistake. If you rinse only with water, the residual water dilutes your titrant and throws off the concentration, which makes every subsequent calculation wrong. Always rinse a clean burette two or three times with a small amount of the solution you plan to fill it with.
Overshoot at the endpoint is the final common issue. Students (and sometimes seasoned analysts) add titrant too quickly near the equivalence point and blow past it. This is less about the burette’s precision and more about the operator’s patience. Experienced analysts slow to half-drop additions near the endpoint, using the stopcock to hang a partial drop on the tip and then touching it off against the flask wall.
How a Burette Compares to Other Ways of Measuring Liquid
People sometimes wonder why you would bother with a burette when a graduated cylinder or a pipette can also measure volumes. The distinction comes down to what kind of measurement you need.
A graduated cylinder measures a fixed or variable volume of liquid that you pour in and read. It is good for measuring out “about 50 mL” of something but is not designed for high precision. A typical 50 mL graduated cylinder has a tolerance of ±0.5 mL, ten times worse than a Class A burette of the same nominal size. You would never use one for a titration.
A volumetric pipette delivers a single fixed volume with high accuracy, comparable to a burette. A 25 mL Class A volumetric pipette has a tolerance of about ±0.03 mL. But it delivers one volume only. If you need to measure an unknown, variable amount of liquid, a pipette is the wrong tool. A burette lets you deliver any volume from zero to its maximum capacity, reading the exact amount at the end. That variable-delivery feature is what makes it indispensable for titrations.
Graduated (Mohr) pipettes offer variable volumes too, but they are designed for one-time delivery of a chosen amount, not for the slow, controlled addition that a titration requires. You could not easily drip reagent into a flask drop by drop from a graduated pipette while swirling and watching an indicator change color. The stopcock on a burette is specifically engineered for that kind of fine flow control.
Choosing the Right Size for a Specific Job
If you are setting up a new titration and wondering what size burette to reach for, the goal is to use the smallest burette that can deliver enough titrant for your sample without needing a refill. Smaller burettes have finer graduations relative to their capacity, giving you better relative precision. But if you have to stop mid-titration, refill, and resume, you introduce a second reading and a second source of error, which can wipe out the precision advantage.
A practical rule: estimate the expected titrant volume for your sample concentration and choose a burette where that volume falls in the upper half of the scale. If you expect to use about 30 mL, a 50 mL burette is the obvious choice. If you expect to use 8 mL, a 10 mL burette delivers better precision, but a 25 mL burette gives you a comfortable safety margin with only a small sacrifice in reading resolution. If your expected volume is under 3 mL, a microburette is the right tool.
In automated and industrial settings, the choice is often dictated by throughput. A digital burette with a 50 mL cartridge might handle a hundred samples in a shift without the operator thinking about refills, while a 10 mL cartridge would need frequent swaps. Convenience and consistency win over marginal precision gains when the instrument’s electronics are already more precise than a human eye reading a meniscus.
When Your Burette Needs Calibration
Glass burettes do not go out of calibration the way electronic instruments do, since their volume markings are etched into the glass and the glass itself does not change shape under normal conditions. But the effective delivered volume can drift if the stopcock becomes worn, if the bore develops scratches that trap liquid, or if chemical etching from aggressive reagents roughens the inner surface over years of use. Laboratories that follow formal quality systems typically verify their burettes periodically by weighing the water delivered at several points along the scale and comparing to the expected mass. If the measured volumes fall outside the Class A tolerance, the burette is retired or reclassified.
Digital burettes require calibration checks more regularly because they rely on a piston mechanism that can wear. Most manufacturers recommend verification every few months or after a set number of dispensing cycles. The good news is that recalibration on a digital burette is usually a software procedure rather than a trip to the metrology lab. You dispense a known number of strokes, weigh the water, and the instrument adjusts its internal volume-per-step calculation accordingly.