FREE CALCULATORS › USP <41> MINIMUM WEIGHT
USP <41> calculator: repeatability and minimum weight
Paste the 10 weighings of your repeatability test: you get the standard deviation, the repeatability check, the minimum weight of your balance - and the accuracy (USP) or sensitivity (Ph. Eur.) check.
How it is calculated
s = standard deviation of the weighings (n - 1); a value below 0.41 d counts as 0.41 d repeatability: 2 × s / smallest net weight ≤ 0.10 % minimum weight = 2000 × s accuracy (USP <41>): |reading - weight| / weight ≤ 0.10 % (weight ≥ 5 % of Max) sensitivity (Ph. Eur. 2.1.7): |reading - weight| / weight ≤ 0.05 %
Example: d = 0.1 mg and a standard deviation of 0.08 mg - above 0.41 d (0.041 mg), so it counts as it is. Minimum weight = 2000 × 0.08 mg = 160 mg. A sample of 50 mg is below it: the balance is not good enough for that weighing by the pharmacopoeias.
The values come from the texts of USP <41> and Ph. Eur. 2.1.7 as we read them - check them against the official chapters of your edition. How often you test is set by your own risk assessment and SOP.
On the scale it is done while you weigh
The routine check before use of UP↑SCALE takes every value from your balance by itself as soon as it is stable, says PASS or FAIL with the USP <41> or Ph. Eur. 2.1.7 profile and keeps the log on the scale. A failed check warns on every device until a re-test passes; the minimum weight warning, users with roles, a tamper-evident audit trail and sealed reports come with ENTERPRISE. The routine check in detail.
More for Laboratories & pharmacies · open the free app · does my scale work?
USP <41> and minimum weight: questions and answers
How do I calculate the minimum weight of a balance?
Minimum weight = 2000 × the standard deviation of 10 weighings of one test weight, where a standard deviation below 0.41 d counts as 0.41 d. It follows from the USP <41> rule 2 × s / m ≤ 0.10 %.
What is the 0.41 d rule?
A balance can not show a spread smaller than its rounding to d. So USP <41> and Ph. Eur. 2.1.7 replace a standard deviation below 0.41 d by 0.41 d. For d = 0.1 mg the smallest s is 0.041 mg, and the smallest possible minimum weight 82 mg.
What is the difference between USP <41> and Ph. Eur. 2.1.7?
The repeatability test is the same. USP <41> tests the accuracy with a limit of 0.10 %, Ph. Eur. 2.1.7 the sensitivity with 0.05 %; both with a weight of at least 5 % of Max.
Which test weight do I use for the repeatability test?
One weight of a known class (e.g. OIML R 111), weighed 10 times - and for the accuracy or sensitivity a second weight of at least 5 % of Max. Which weights exactly is set by your SOP and the chapter of your edition.
Is a balance below the minimum weight wrong?
Not wrong, but not good enough for that weighing: below the minimum weight the relative uncertainty of a result is bigger than the pharmacopoeias allow. Weigh a bigger sample or use a finer balance.
More free calculators
No sign-up, nothing is sent anywhere - the maths runs in your browser. All calculators
Roast loss calculator
The roast loss in %, what a kg of roasted coffee costs you and how much green coffee an order needs.
℮ calculator: TNE, T1, T2
The limits for your nominal quantity, the sample plan for your lot - and the lot check of your weights.
Gold value & density test
Fine gold, value and payout of a piece by karat - and the density test that spots fakes.
Dough temperature (DDT)
The water temperature for your desired dough temperature, with the friction of your mixer.
Cannabis infusion & dose
mg THC and CBD per gram of your butter, oil or tincture - and the infusion for a dose per portion.