Test weight for Canadian grains
Test weight is the measure of grain density determined by weighing a known volume of grain. It is a grading factor for many grains under the Canada Grain Act. Test weight is a measure of density (a measure of mass given in volume). It is not a measure of weight or quantity.
Determining test weight
In Canada, test weight is assessed after dockage is removed, as defined in the cleaning procedures for each class of grain. Test weight for corn is determined before removing cracked corn and foreign material.
Test weight is expressed as either kilograms per hectolitre (kg/hL) or grams per 0.5 litre (g/0.5L).This is the official measure in Canada. The Official Grain Grading Guide specifies minimum test weights required to make grades for certain grains.
Samples are graded Sample Account Light Weight only if the test weight is lower than the minimum test weight established for that class of grain, and in accordance with the Order of Precedence in the Glossary of the Official Grain Grading Guide.
Grain test weight is commonly referred to as bushel weight and expressed as pounds per bushel (lb/bu). Bushel weights may be distinguished as pounds per bushel Avery (lb/bu A) or pounds per bushel Winchester (lb/bu W). The Winchester bushel volume is smaller than the British bushel volume that is used to calculate the Avery bushel used in Canada. There is also a difference in how the effect of grain compaction is treated.
Bushel weight in Canada
The Avery bushel is used in Canada. 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.
Bushel weight in the United States
The Winchester bushel is used in the United States. The Winchester bushel weight is based on the United States bushel volume (35.24 L). The equipment used does not allow for release of air pockets to account for better grain compaction. The effect of compaction can be significant because it is influenced by the density of the grain.
Make sure you know 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 2 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, 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 bushel (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 it will not meet a specification for 45.5 lb/ W bu.
Imperial, Avery and Winchester bushels
- The British Imperial bushel is 36.369 liters (or 1.2843 cubic feet)
- The Avery bushel is the Imperial bushel, but the weight conversion accounts for grain compaction
- The Winchester bushel is 35.239 liters (or 1.244 ft3)
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|
|No. 1 Canada Western General Purpose barley||303||63.0||49.1||50.5||47.0|
|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
Converting grams per 0.5 litre to pounds per Winchester bushel is 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.
These test weight conversions are the same in all of the conversion charts.
|g/0.5 L||lb/W bu|
Conversion factors and different grains
Different grains have different densities, so all grains have different conversion factors. When converting from grams per 0.5 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. There are 2 methods for converting test weight to larger volumes.
Straight mathematical conversion
Multiply the weight to match the new volume. This conversion method does not take into account the compaction of grain that occurs when measured in larger volume containers.
Mathematical conversion based on calibration to a 100-litre volume
Use the Canadian Grain Commission’s test weight conversion charts. These charts equate grams per 0.5 litre weights to weight per hectolitre 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.
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