Guide · Buyer guides
Is my pound short? Scales, moisture loss and fair weight checks
A pound of THCA flower should net 453.6 g after you subtract the packaging. A bag that reads a few grams under can still be a full pound once you account for scale error, tare and moisture loss: federal weights-and-measures guidance allows 3% for moisture in packaged cannabis, which is 13.6 g on a pound.
Reviewed 2026-10-03. Figures from NIST Handbook 44 and Handbook 133, 2026 editions. These handbooks bind sellers where a state adopts them; this guide uses them as a fair yardstick, not as a legal test of any order.
The numbers for one pound and one half pound
| Labeled size | Net target | 3% moisture allowance | Handbook 133 MAV for one package |
|---|---|---|---|
| Pound (LB) | 453.6 g | 13.6 g | 19.9 g |
| Half Pound (HP) | 226.8 g | 6.8 g | 12.7 g |
Two federal handbooks set these figures:
- NIST Handbook 133, Chapter 2, Table 2-3, lists “Cannabis” with a 3% moisture allowance. The note defines it as plant material only, whether above or below 0.3% total delta-9 THC, so hemp flower is included.
- Handbook 133, Appendix A, Table 2-5, sets the maximum allowable variation (MAV): 19.9 g for packages labeled more than 426 g up to 489 g, and 12.7 g for more than 208 g up to 263 g.
Inspectors judge a lot of packages, not one bag. The sample’s average must meet the label, and no single package may fall short by more than its MAV. One buyer with one bag can only borrow those numbers as a reference.
Step 1: trust the scale before the bag
A scale has two numbers that matter: the display step (d), and the verification interval (e) that its tolerance is counted in. On most kitchen scales they are the same. Handbook 44, Section 2.20 sets the tolerances for legal-for-trade scales:
| Scale | Interval (e) | A pound in intervals | Maintenance tolerance | Acceptance tolerance (new scale) |
|---|---|---|---|---|
| Class III | 2 g | 227 e | ±2 g | ±1 g |
| Class III | 1 g | 454 e | ±1 g | ±0.5 g |
| Class II | 0.1 g | 4,536 e | ±0.1 g | ±0.05 g |
Table 6 of Section 2.20 allows 1 e of error up to 500 e on a Class III scale and up to 5,000 e on a Class II. Acceptance tolerance is half of that. Table 7a names Class III for “all commercial weighing not otherwise specified” and Class II for laboratory weighing.
A home scale carries no class marking and no legal tolerance. Test it:
- Use a known mass. A calibration weight is best; if the scale came with one, use it.
- Weigh it three times, removing it between readings. All three should match.
- Weigh it at the center and at each corner of the platform.
- Check capacity. A 500 g scale is near its limit with a pound and its bag on it.
Handbook 44’s Table 8 recommends a minimum load of 20 e on Class III scales, because light loads show large relative errors. That is 20 g on a 1 g scale, which a pound clears easily.
Step 2: get the tare right
Most short readings on arrival are tare mistakes. Net weight is gross minus everything that is not flower.
- Weigh the sealed bag as delivered. This is the gross. Photograph the display with the lot label in frame.
- Open the bag and move the flower to a clean container you have already weighed.
- Take out humidity-control packs and desiccants. They are not flower.
- Weigh the empty original bag, with its label and zipper. This is the packaging tare.
- Net = gross − packaging tare. Cross-check it against the flower in your container.
Do not tare the scale with a different bag of a similar size. Bags of the same style can differ by several grams, and that error lands straight on the net.
Step 3: work out what moisture can explain
Flower loses water between packing and weighing, and the dry matter stays the same. If a pound was packed at a known moisture, the shortfall tells you how far it dried:
moisture now = 1 − (packed weight × (1 − packed moisture)) ÷ weight now
Worked example: a pound packed at 453.6 g and 12% moisture.
| Net on arrival | Short by | Moisture now | Drop |
|---|---|---|---|
| 448.6 g | 5 g | 11.0% | 1.0 point |
| 443.6 g | 10 g | 10.0% | 2.0 points |
| 438.6 g | 15 g | 9.0% | 3.0 points |
| 433.6 g | 20 g | 7.9% | 4.1 points |
| 423.6 g | 30 g | 5.8% | 6.2 points |
A 10 g shortfall needs only a two-point drop, which a dry trip can produce. A 30 g shortfall needs the flower to fall to about 6% moisture. Flower that dry is usually brittle, and its stems snap clean.
Water activity is the better measure of where the flower is now. ASTM D8197 sets 0.55–0.65 aw for dried cannabis flower. No single conversion links water activity and moisture percent; the relation differs by lot. If a meter reads inside that range and the bag is still far short, moisture is the weaker explanation.
Step 4: read the result
A working guide for a pound, built from the figures above:
| Net shortfall on a pound | Most likely reason | What to do |
|---|---|---|
| 0–2 g | Scale interval and tare | Nothing; record it |
| 2–13.6 g | Moisture loss within the 3% allowance | Record it; check aw or feel |
| 13.6–19.9 g | Beyond moisture alone, inside one-package MAV | Re-weigh; send photos and figures to the seller |
| More than 19.9 g | Packing or weighing error at the source | Hold the bag apart; contact the seller with the lot number |
For a half pound, use 6.8 g and 12.7 g as the two breakpoints.
Keep a record
- Date and time of each weighing.
- Gross, packaging tare and net, in grams.
- The scale used and the result of its test weight.
- Water activity, if measured.
- Photos: the sealed bag on the scale, the lot label, the empty packaging on the scale.
The same record checks the next order. A pound that arrives 10 g light every time from one source is a packing habit, not transit. Here, short-weight questions go to the Operator with the lot number. What else to check on every lot is in Buying THCA by the pound.
Sources
- NIST Handbook 44 (2026), Section 2.20 Scales: Tables 3, 6, 7a and 8; T.N.3.2.
- NIST Handbook 133 (2026), Chapter 2: Section 2.3.8 and Table 2-3, moisture allowances.
- NIST Handbook 133 (2026), Appendix A: Table 2-5, MAVs for packages labeled by weight.
- ASTM D8197: water activity of dried cannabis flower.
Questions
How much should a pound of THCA flower weigh?
453.6 g net (exactly 453.59237 g), not counting the bag, jar or any humidity pack. A half pound is 226.8 g net.
How much weight can a pound of flower lose to moisture in transit?
NIST Handbook 133 (2026) gives weights-and-measures inspectors a 3% moisture allowance when they check packaged cannabis plant material. On a pound that is 13.6 g; on a half pound, 6.8 g. A bag packed at 12% moisture that dries to 10% loses about 10 g.
Is a kitchen scale accurate enough to check a pound?
Often, if it reads in 1 g steps, holds at least 500 g, and reads a known test weight correctly. A legal-for-trade Class III scale with a 1 g interval may be off by up to 1 g at a pound in service. Test any scale with a known weight before trusting it.
What should I do if my pound is short?
Photograph the sealed bag on the scale with the lot label visible, weigh the empty packaging, and write down the net figure and date. Check moisture. Then contact the seller with the lot number and the photos before mixing the flower with other stock.