Test weight for Canadian grains
What is test weight?
Test weight is the measure of grain density determined by weighing a known volume of grain. In Canada's grain grading specifications, it is expressed in grams per 0.5 litre or kilograms per hectolitre. Test weight is a grading factor for many grains under the Canada Grain Act. Despite the name, test weight is not a measure of weight or quantity, but is a measure of density (a measure of mass in a given volume).
In the current Canadian grading system, test weight is assessed after dockage is removed and is expressed as kilograms per hectolitre, kg/hL (kilograms per 100 litres of volume), or as g/0.5L (grams per half-litre). This is the official measure in Canada, and the Official Grain Grading Guide issued by the Canadian Grain Commission specifies minimum test weights required to make grades for certain grains.
In Canada, grain test weight is officially expressed in metric units of kilograms per hectolitre (kg/hL), which may commonly be referred to as "bushel weight" and expressed as pounds per bushel (lb/bu). However, bushel weights may be distinguished as pounds per bushel 'Avery' (lb/bu A) or pounds per bushel 'Winchester' (lb/bu W). The Avery bushel weight is based on the British 'Imperial' bushel volume (36.37 L) in which the official method and equipment allows for release of air pockets from compaction of grain in the container. In contrast, the Winchester bushel weight is based on the U.S. bushel volume (35.24 L) and the equipment used does not allow for release of air pockets to account for better grain compaction. The effect of compaction can be significant as it as influenced by the density of the grain.
Importance of test weight
A bushel of wheat in Canada may not be equal to a bushel of wheat in the United States. The Winchester bushel volume is smaller than the British bushel volume that is used to calculate the Avery bushel used in Canada.
In addition to the difference in volume, there is a difference in how the effect of grain compaction is treated. In Canada, determining test weight takes compaction into account, and conversion of the official metric test weight measure to pounds per bushel is based on the Imperial bushel, and is referred to as pounds per bushel-Avery. Conversion of the official metric test weight measure to pounds per bushel based on the Winchester bushel does not take compaction into account, and is referred to as pounds per bushel-Winchester. Therefore, it is critical to make sure which type of bushel is being used when making formal grain transactions.
If you are selling your grain by contract to a company in the United States, test weights specified in the contract are in pounds per bushel. Usually, this means the Winchester bushel. However, if you get a test weight measurement for your grain at a primary elevator in Canada, it will be in Avery bushels. The difference between the two bushels could mean a loss for you.
Example: Difference between the units of measurement
If the contract for Select CW two-row barley specifies a test weight of 45.5 lb/bu, this means that it is 45.5 pounds per Winchester bushel (45.0 lb/W bu). The equivalent test weight in the test weight conversion chart for barley is 48.8 pounds per Avery bushell (lb/A bu). Therefore, any shipment of barley with a Canadian test weight of less than 48.8 lb/A bu will not meet the United States contract specifications.
Conversely, the Canadian test weight of 45.5 A lb/ bu is equivalent to 42.4 lb/W bu. so will not meet a specification for 45.5 lb/ W bu.
Imperial, Avery and Winchester bushels
The Imperial bushel is 36.369 litres (or 1.2843 ft3). It is the British bushel and is commonly used by Canadian producers. In the table below, the figures showing conversion to Imperial are approximate values.
The Avery bushel is the Imperial bushel, but the weight conversion accounts for grain compaction. It is in use in Canada.
The Winchester bushel is 35.239 litres (or 1.244 ft3) and is in use in the United States.
The following table shows how these measurements differ in reference to test weights of specific grains and grades.
|Measurement in:||g/0.5 L||kg/hL||lb/Imperial bushel (approx.)||lb/Avery bushel||lb/Winchester bushel|
|Special Select Canada Western two-row barley||303||63.0||49.1||50.5||47.0|
|Special Select Canada Western six-row barley||298||62.0||48.3||49.7||46.2|
|No. 1 Canada Western Red Spring wheat||365||75.0||58.2||60.1||56.6|
|No. 1 Canada Western Amber Durum wheat||387||79.0||61.5||63.3||60.1|
Converting to Winchester bushels
Conversions from grams per half litre to pounds per Winchester bushel involve a straight mathematical conversion. The conversion doesn't account for grain compaction because the weight per small volume is simply multiplied to reach the larger volume. The same conversions are used for each crop.
This range of conversions is the same in all the tables.
|g/0.5 L||lb/W bu|
Conversion factors and different grains
Different grains have different densities. As a result, all different grains have different conversion factors. When converting from grams per half litre to pounds per Avery bushel, there is no single conversion factor that can be applied to all grains.
Make sure to use the conversion factors and methods appropriate for the grain being measured.
Conversion to larger volumes
Following the test weight procedures, a weight is obtained for the 0.5 litre volume of grain. However, the weight of grain in a 0.5 litre container must be converted to more meaningful volumes that are much greater than a 0.5 litre.
Two methods can be used:
- Straight mathematical conversion: Simply multiply the weight to match the new volume. This does not take into account the compaction of grain that occurs when measured in larger volume containers.
- Mathematical conversion based on calibration to a larger (100-litre) volume: The Canadian Grain Commission produces calibration charts that equate grams per 0.5 litre weights to weight per hectolitre (i.e. per 100-litres) using a conversion formula. As the weights are extended from per 0.5 litre to per hectolitre, compaction is taken into account. Compaction occurs as the grain's weight causes it to become more densely packed, and air pockets disappear.
Test weight is determined after the removal of dockage as defined in the cleaning procedures described for each class of grain.
Test weight on corn is determined prior to removal of cracked corn and foreign material.
Samples are graded Sample Account Light Weight only if the test weight is lower than the minimum established for that class of grain and in accordance with the Order of Precedence as stated in the Glossary section of the Canadian Grain Commission's Official Grain Grading Guide.
For more information please contact Statistics and Business Information.
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