Analytical Balances: How to Choose One and Why Readability Is Not Accuracy
- Jul 30
- 7 min read
Updated: 3 days ago
Key Summary
Readability is not accuracy. An analytical balance reading to 0.1 mg does not mean it is accurate to 0.1 mg. Readability is simply the smallest increment the display shows. Accuracy is governed by repeatability, linearity and how well the balance is sited.
The specification that actually matters is minimum weight. Below a certain sample mass, the balance’s own uncertainty exceeds your tolerance and the result is not fit for purpose. USP <41> makes this a compliance requirement, not a preference, and it is the reason a more expensive balance is sometimes the only correct answer.
Analytical balances in our range run from £1,168.50 to £4,313.00, and every one of them reads to 0.1 mg.
What is an analytical balance?
An analytical balance is a high-precision laboratory balance that reads to 0.1 mg, or 0.0001 g, and is enclosed in a draught shield to protect the weighing pan from air currents. Capacities are typically 100 g to 300 g, because precision and capacity trade against each other.
The draught shield is not a cosmetic feature. At 0.1 mg resolution, a door opening across the room is enough to move the reading. Anything that reads to 0.1 mg without an enclosure is not an analytical balance, whatever it is called.
Where analytical balances sit among the classes:
Class | Readability | Typical capacity | Used for |
Micro | 0.001 mg | 2–10 g | Trace and forensic work |
Semi-micro | 0.01 mg | 50–100 g | Reference standards, potency assays |
Analytical | 0.1 mg | 100–300 g | The laboratory default |
Precision | 1 mg or 10 mg | 300 g–8 kg | Bulk reagents, media preparation |
Industrial and floor | 1 g upwards | 10 kg upwards | Goods in, bulk materials |
Most laboratories need an analytical balance and a precision balance, rather than a single balance that tries to do both jobs. If you are not yet sure which class you need, a guide to choosing a
laboratory balance is the right read for you.
Readability, repeatability, linearity: what is the difference?
Readability is what the display shows. Repeatability, linearity, and eccentricity are what determine whether the number is right.
Readability (d) is the smallest increment displayed, 0.1 mg on an analytical balance. It is a display property, nothing more.
Repeatability is the standard deviation you get weighing the same object repeatedly. This is the single most useful accuracy figure, because it drives the minimum weight calculation below.
Linearity is how far the balance deviates from a true straight line across its range. A balance can be repeatable and still read consistently high at one end.
Eccentricity, or corner load, is the error introduced when the sample is off-centre on the pan. Real, easily measured, and easily avoided by centring the sample.
Sensitivity drift is how the reading changes with temperature. This is what internal calibration compensates for.
Two balances can both read to 0.1 mg and differ substantially in repeatability. That difference is most of what you are paying for as you move up the range, and it is why the question “how many decimal places?” is the wrong question.
What is minimum weight, and why does it matter?
Minimum weight is the smallest sample you can weigh and still meet your required accuracy. Below it, the balance’s own uncertainty is a larger share of the reading than your tolerance allows.
The logic is simple. Balance uncertainty is roughly constant in absolute terms, so as the sample gets smaller, that fixed error becomes a larger percentage. Weigh 100 mg with an uncertainty of 0.1 mg and you are at 0.1%. Weigh 5 mg with the same uncertainty and you are at 2%.
USP <41> Balances turns this into a requirement. For substances weighed for quantitative analysis, measurement uncertainty must be no more than 0.10% of the amount weighed, determined from repeatability. In practice:
Minimum weight ≈ 2 × (repeatability standard deviation) ÷ 0.001
So a balance with a repeatability of 0.05 mg gives a minimum weight of about 100 mg. If your method requires you to weigh 20 mg of reference standard, that balance is not compliant for the task no matter what its display shows. USP <1251> Weighing on an Analytical Balance is the companion guidance chapter.
This is the most useful thing to take from this page. When you ask a supplier for a quotation, give them your smallest routine sample weight, not the number of decimal places you want.
Internal or external calibration: which do I need?
Internal calibration uses a motorised weight built into the balance. External calibration uses a certified weight you place on the pan. Both adjust the balance’s sensitivity. Neither is a substitute for a traceable calibration certificate.
Three distinct things get confused here:
Adjustment, often loosely called calibration, corrects the balance’s sensitivity against a reference weight. Internal systems can do this automatically on a temperature change or a timer.
Routine user checks with a certified test weight confirm the balance is still performing between services. Do these daily or weekly, and record them.
Traceable calibration is a documented measurement by an accredited laboratory, producing a certificate with stated uncertainty. This is what an auditor asks for.
Internal calibration is worth having if your lab temperature swings, if the balance is used by many people, or if you cannot rely on someone remembering to run a weight. It removes the commonest source of drift.
Test weights are classified by tolerance, OIML classes E1, E2, F1 and F2 in descending order of accuracy, with equivalent ASTM classes. As a rule the test weight should be substantially more accurate than the balance you are checking. Weight sets are available in our balance accessories.
Our ISO 17025 calibration service covers traceable balance calibration on site, alongside the rest of your equipment schedule. Accreditation is what makes a certificate defensible in audit, and you can check any provider’s scope on the UKAS website.
Where should an analytical balance be installed?
On a heavy, vibration-free bench, in a corner, away from doors, walkways and air conditioning. Siting is free and it affects your results more than the next £1,000 of specification.
Vibration. A stone or dedicated anti-vibration bench, not a wooden bench shared with a centrifuge or a shaker
Air movement. Away from doors, windows, fume cupboards and HVAC outlets. Even with the shield closed, pressure changes matter
Temperature. Stable. Avoid direct sunlight and radiators. Allow the balance to warm up after switching on, and let samples equilibrate to room temperature before weighing
Static. The hidden cause of drifting readings. Plastic weighing vessels, dry powders and low humidity generate charge that pushes the reading around. An anti-static ioniser fixes what better technique cannot
Level. Check the spirit level after any move. An unlevelled balance is a mis-reading balance
Bench space. Leave room to work either side. People wedge balances into corners and then knock them
Weighing best practice
Handle the sample, not the balance.
Use tongs or gloves for weighing vessels. Fingerprints add mass and moisture
Centre the sample on the pan to avoid corner-load error
Close the draught shield and wait for the stability indicator, do not read through the motion
Tare with the vessel in place, then add the sample
For volatile or hygroscopic samples, weigh by difference and work quickly
Record the balance ID and the date on the result, so a later calibration issue can be traced to affected data
Clean spills immediately. A grain of powder under the pan is a systematic error
Analytical balances from LS Scientific
Five models, all reading to 0.1 mg. Prices verified 29 July 2026 and include sale reductions.
Model | Was | Price |
£1,230.00 | £1,168.50 | |
£1,675.00 | £1,591.25 | |
£2,955.00 | £2,807.25 | |
£3,950.00 | £3,752.50 | |
£4,540.00 | £4,313.00 |
How to read that ladder. All five display 0.1 mg. What rises with price is repeatability, and therefore minimum weight, along with build quality, draught shield design, calibration features, data handling and connectivity. If you weigh 100 mg samples routinely, the entry models are appropriate. If you weigh 20 mg reference standards for a regulated assay, work up the range and ask for the repeatability figure before you commit.
Also in the weighing category: semi-micro balances for 0.01 mg work, precision balances for bulk weighing, moisture analysers, portable scales, floor scales and balance accessories.
Tell us your smallest routine sample weight and your accuracy requirement and we will tell you which model meets it. Talk to our technical team.
Frequently asked questions
What is an analytical balance used for? Weighing small quantities to 0.1 mg, typically reference standards, reagents for volumetric solutions, active pharmaceutical ingredients and samples for quantitative analysis.
What is the difference between an analytical balance and a precision balance? An analytical balance reads to 0.1 mg with a draught shield and a capacity of 100–300 g. A precision balance reads to 1 mg or 10 mg with a higher capacity, up to several kilograms. Use the analytical balance for small samples and the precision balance for bulk.
What does readability mean on a balance? The smallest increment the display can show, 0.1 mg on an analytical balance. It is not the same as accuracy, which depends on repeatability, linearity and installation.
What is minimum weight on an analytical balance? The smallest sample you can weigh while still meeting your accuracy requirement. Under USP <41> it is approximately twice the repeatability standard deviation divided by 0.001. A balance with 0.05 mg repeatability has a minimum weight of about 100 mg.
How often should an analytical balance be calibrated? Traceable calibration annually as a minimum, plus routine user checks with a certified test weight daily or weekly depending on use. Recalibrate after any move.
Why does my balance reading keep drifting? The usual causes are static on plastic vessels or dry powders, air movement from a door or air conditioning, temperature difference between sample and room, vibration from nearby equipment, or a balance that has not been levelled after a move.
Do I need internal calibration? It is worth having where lab temperature varies, where several people share the balance, or where routine weight checks might be missed. It corrects sensitivity drift automatically.
How much does an analytical balance cost in the UK? Between £1,168.50 and £4,313.00 in our range. All five models read to 0.1 mg, and the price difference reflects repeatability, build and features rather than display resolution.
References and standards
USP <41> Balances. Sets the requirement that measurement uncertainty must not exceed 0.10% of the amount weighed, and defines the minimum weight concept.
USP <1251> Weighing on an Analytical Balance. Companion guidance on installation, qualification and routine use.
OIML R76 and EN 45501, non-automatic weighing instruments. The metrological framework, relevant where a balance is used for legal-for-trade weighing.
OIML R111, weights of classes E1, E2, F1, F2, M1. Defines the test weight classes referenced above.
United Kingdom Accreditation Service (UKAS). Check the accreditation scope of any calibration provider before accepting a certificate.
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