Agriculture & Future Food Systems · Article
Choose a measurement method and keep its gaps visible
Weighing, diaries and estimates can complement each other, but their coverage and uncertainty must stay attached to the results.
Preparation and related reading
Shared Foundations
Related articles
This article helps you
- Exclude container mass from a direct weighing.
- Distinguish measured quantities from converted estimates.
- Keep missing records separate from recorded zeroes.
A bin and a diary see different things
A kitchen can weigh its collected food material, while a household diary records individual disposal events and their reasons. Both can be useful. They need not cover the same routes: a collection-bin study can miss material going elsewhere, and a diary can miss an event that nobody records.
Choose the method for the question and access available. Direct weighing observes a mass under specified conditions. A diary is a record-keeping arrangement that can contain weighed amounts, counts, volumes or guesses. Calling something a diary does not tell us how each quantity was obtained.
Weigh the intended material
A scale reading can include a container, liner or unrelated material. Define the contents to be measured, exclude tare and record the unit. Suitable equipment and correct use matter, but a precise scale cannot identify an omitted route or an unrepresentative collection period.
In an invented case, the filled container reads 3.40 kg and its empty container plus liner reads 0.40 kg. Net material is 3.00 kg. The diagram follows this subtraction and the record it produces. It assumes no other material to exclude; it does not establish a typical waste quantity.
A weighing with tare removed
Read the diagram as text
An invented 3.40 kg gross reading and 0.40 kg container-and-liner tare give 3.00 kg net material. The inventory records the net amount and its scope.
Parts
- Gross: 3.40 kg
- Container, liner and in-scope contents.
- Tare: 0.40 kg
- Empty container and liner.
- Net: 3.00 kg
- 3.40 − 0.40; no other material assumed.
- Record net and scope
- Keep units, period and exclusions with the quantity.
Connections
- Gross: 3.40 kg → Net: 3.00 kg: gross
- Tare: 0.40 kg → Net: 3.00 kg: subtract
- Net: 3.00 kg → Record net and scope: record
Keep conversions explicit
Counts or volumes can be converted to mass only with a stated relationship. Identical weighed units make a count useful; varied items need an appropriate estimate of average mass. Volume also requires a density relevant to the material and its condition.
The FLW methods guidance distinguishes these approximations from direct weighing. Record the count, conversion factor and resulting mass, not just the final number. If the factor comes from a sample, its representativeness matters. A tidy multiplication does not remove uncertainty in the factor.
A diary can link quantities to reasons
A diary can record when food was discarded, what it was, the amount and the reported reason. EPA's tracking-tool overview likewise connects quantities and reasons to practical changes. Such detail can help ask better questions than a combined bin total alone.
The FLW diary guidance names omissions, approximated amounts and changed behaviour during recording as limitations. A participant may become more attentive to waste because the diary is being kept, or another household member may discard food without an entry. The record is evidence about the recording period, not an automatic measure of ordinary behaviour.
Distinguish a missing entry from zero
Suppose a seven-day diary has six complete daily records totalling 2.40 kg and one missing day. The mean for the six recorded days is 0.40 kg per recorded day. The seventh day cannot be entered as zero merely to complete the sheet.
A recorded zero means the participant observed no in-scope material for that period. A blank can mean no material, forgotten recording or missing observation. Clarify the distinction during collection. If a missing value is estimated, label the method and uncertainty instead of presenting it as directly measured.
Combine records without double counting
Methods can complement one another when the scope and material identity are clear. A diary might capture a route outside a bin study, or help interpret why material entered the bin. Do not add the diary entry to the bin mass when they describe the same discarded food.
Keep measured, converted and reported information identifiable. Document exclusions and gaps, then repeat measurements consistently if monitoring change. Use the shared measurement Foundation for uncertainty and the adjacent articles for stage boundaries, fractions and representative periods. The method should make the result understandable, including what it could not observe.
Worked examples
Record net mass
An invented filled container reads 3.40 kg; its empty container and liner read 0.40 kg. What is the in-scope net mass if no other material is present?
- Subtract tare: 3.40 − 0.40 = 3.00 kg.
- Record the net mass with the unit and material scope.
- Do not include the empty container again in a fraction total.
The stipulated net material is 3.00 kg. Correct tare does not establish complete route coverage.
Use only the observed-day denominator
Six complete diary days total 2.40 kg; a seventh day is missing. What mean can be calculated directly?
- Calculate 2.40 kg ÷ 6 recorded days = 0.40 kg per recorded day.
- Keep the seventh day marked missing.
- A total or mean for the complete seven-day period needs information or a disclosed estimation method for that day.
0.40 kg per recorded day for the six observed days. It is not a complete weekly mean.
Check your understanding
Twelve items are counted. An assumed relevant average mass is 90 g per item. What converted estimate results?
Show answer and reasoning
1,080 g, or 1.08 kg.
12 × 90 = 1,080; the arithmetic is exact for the assumed factor, but actual item masses may vary.
Does a highly precise scale establish that all disposal routes were included?
Show answer and reasoning
No.
Instrument precision and inventory coverage are different questions.
A diary entry and a bin reading describe the same food. Should their masses be added as separate waste?
Show answer and reasoning
No.
The observations must be reconciled, not counted as two material flows.
Key ideas
- Record tare, scope and units with weighed quantities.
- Expose conversion assumptions and diary omissions.
- Treat missing data as missing and reconcile overlapping records.
References
Sources supporting the explanations and examples in this article.