Corn Test Weight Explained
What is test weight?
Key Points
 Test weight is the measure of
bulk density, or the weight of a
specified volume of corn.
 In addition to density, other
factors that influence test
weight include: kernel size and
shape, slickness of seedcoat,
and physical characteristics.
 High test weight corn is more
desirable in quality because it
means the kernels are a higher
percentage hard endosperm.
 Factors contributing to lower
Test weight is the measure of bulk density, or the weight of a specified volume of corn. It is just
one of the quality tests run on corn that can have an effect on premiums or discounts received at
sale. Corn in the United States is sold on a weight basis in a 56 pound block called a ‘bushel’.
Historically, a bushel is a measure of volume, not weight, equivalent to 32 quarts or 1.2445 cubic
feet. However, because the logistics of selling by weight make more sense than by volume, a
standard was set that each 56 pound measure of corn would be considered a bushel.
So, how does test weight come into the picture? Test weight helps to quantify differences in grain
density that may result from differences in environmental conditions or production practices.
Since test weight is the measure of the weight of a specified volume, it takes into account the
density of each kernel as well as the density with
Table 1. Test weight minimums
which they are packed together in the measurement
for U.S. corn grades
vessel. Test weight is measured by filling a
standardized one quart vessel with corn until spilling
Minimum Test
U.S. Grade
over. The tester then levels the corn and measures
Weight (lb/bu)
the weight. There are 32 quarts in one volume
U.S. No. 1
56.0
bushel, so the result is multiplied by 32 to convert
from pounds per quart to pounds per bushel.
U.S. No. 2
54.0
In 1916, the United States Grain Standards Act was
passed by Congress specifying grades and grade
requirements, including test weight minimums for
each grade of corn. These are shown in Table 1.
Price penalties vary for grain with test weights below
the minimum lb/bu value. The minimum test weight
for U.S. No. 1 grade corn is 56 pounds, thus the 56-pound bushel measurement.
test weights include: grain
moisture, stresses that reduce
seed fill, and ear rots.
U.S. No. 3
52.0
U.S. No. 4
49.0
U.S. No. 5
46.0
Source: Grain inspection handbook. 2013.
U.S. Department of Agriculture Grain Inspection,
Packers and Stockyards Administration.
Book II—Corn. www.gipsa.usda.gov/
What factors influence the test weight of corn?
Corn test weights can range from 45 – 60 pounds per bushel. Various physical factors can influence test weight, but the primary one is moisture.
Because kernel dry matter is more dense than water, proportionally as the amount of water decreases, the bulk density of the kernel increases.
Therefore, there is an inverse relationship between test weight and moisture; test weight increases as moisture level decreases.
Test weight, however, is not only a function of density. When density reaches a certain point, other factors determine test weight: how well kernels
fit together (size and shape), how slippery the seedcoats are, and other physical characteristics. In some cases, seeds that fill a little longer and get
heavier can actually lose test weight due to shape changes. Drying from 28% to 20% moisture content generally results in an increase in test
weight because seeds shrink and get denser. A change from 20% to 15%, however, can actually decrease test weight in some cases because
kernels can lose moisture weight without a change in size or shape.3
How much the test weight increases upon drying varies based on the corn product, grain condition, and drying temperature. Although the cause is
not fully understood, studies have shown that slow drying with natural or low-heat air can result in greater increases of test weight than fast drying
with high heat. Test weight can also be a good indicator of storability, as it generally decreases as grain deteriorates. Corn below 54 pounds per
bushel after drying should not be stored into warm weather and should be dried to less than 15% moisture content for any type of storage.2
Corn products will vary in test weight due to their unique endosperm makeup. This variability does not necessarily correspond to differences in
genetic yield potential. Test weight for a given corn product may vary by location or season, but does not necessarily correspond to the yield level
of an environment. Test weights of corn products that differ greatly in kernel moisture percentage should not be compared
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Corn Test Weight Explained
to one another, because the drier product has an unfair advantage in that comparison. In order to learn more about test weights in your fields or for
help choosing corn products, consult with your Channel Seedsman.
What are the implications of high versus low test weight?
High test weight corn is more desirable in quality because it means the kernels are a higher percentage of hard endosperm; whereas lower test
weight usually indicates that the crop did not mature entirely or was subjected to stresses. When it comes to the logistics of grain handling, it also
makes sense as to why higher test weight corn is more desirable. Transportation and storage of low test weight grain is more expensive per pound,
thus it is often discounted by buyers. Higher weight in a smaller volume is advantageous in handling and storage as well as during harvest because
more weight bushels will fit in the truck,
Table 2. Example calculation of corn value, with different test weights.
bin, or grain tank of the combine.
Occasionally, there is confusion regarding
how drying your grain can increase its
value. Sometimes claims are made
implying that drying (resulting in test weight
increase) can increase the weight of grain
that can be sold. At sale, 56 pounds is 56
pounds, regardless of the test weight.
Higher test weight corn just takes up less
volume because it is denser and packs
more tightly. Price paid is impacted when
test weight is low enough to incur a price
penalty per bushel (Table 2, Load 3). In
some cases, a premium may be paid for a
higher test weight. An increase in price is
never due to an increase in the weight of
corn sold.
Load 1
Load 2
Load 3
Weight (lbs)
20,000
20,000
20,000
Number of bushels to
be sold
357.14
357.14
357.14
Moisture content
14.5%
14.5%
14.5%
Test weight (lb/bu)
54.0
59.0
51.0
Volume (ft3)
461
422
488
Price ($/bu)
4.00
4.00
4.00-0.04 = 3.96
Calculation of value
357.14 bu x 4.00
357.14 bu x 4.00
357.14 bu x 3.96
Value ($)
$1,428.57
$1,428.57
$1,414.27
Source: Bern, C. and T. Brumm. 2009. Grain test weight deception. Iowa State University Extension. PMR
1005. http://lib.dr.iastate.edu/
What are the causes of low test weight?
As previously stated, there is an inverse relationship between grain moisture and test weight. Test weight increases naturally as kernel moisture
content drops as long as the kernel remains intact. As moisture is shed (to a certain point), volume shrinks and drier grain is slicker which results in
better packing. When corn comes out of the field at higher moisture contents, it makes sense that test weights may be less than ideal. This is the
one cause of low test weight that can be remedied to a certain extent by drying.
Other factors contributing to lower test weights include any plant stresses that impact the movement of nutrients to the kernel during grain fill or
degrade the integrity of the kernel once it is filled. Plant diseases, insects, soil fertility, and environmental conditions can all ultimately influence test
weight. Stress that slows or halts grain fill can result in kernels with low density endosperm which results in low test weight. The types of stresses
affecting test weight include:4
 Drought stress, late-season foliar diseases, and low fall temperatures can all cause a reduction of photosynthetic production. This can result in
less than optimum starch deposition in kernels and may even prevent plants from completing grain fill.
 Early frost or freeze that results in leaf or whole plant death ends grain filling, essentially having the same effect.
 Ear rots that cause kernel damage can result in lightweight chaffy grain, as well as broken kernels, and excess foreign material (this low test
weight grain has other overarching problems aside from just low test weight).
Research was done at the University of Minnesota to asses the effect on test weight of plant death at different stages of development prior to
natural black layer formation. It was found that test weight will vary based on the stage corn had reached before grain fill was ended. Immature ears
were taken at various stages from soft dough through full maturity and dried at 80 and 120 °F. The study showed that those kernels that had
reached soft dough and early dent actually decreased test weight after drying, whereas there was an expected increase at all other stages.
Increase in test weight will depend on stage of development, kernel moisture and grain quality, and drying temperature. The general result of this
study found that if corn is well dented or beyond in maturity, some increase in test weight should occur with drying.1
Sources: 1 Hicks, D. 2004. Corn test weight changes during drying. Minnesota Crop News. http://blog.lib.umn.edu/efans/cropnews/ (verified 8/22/14); 2 Hurburgh, C. and R. Elmore. 2008. Corn
quality issues in 2008 – moisture and test weight. Integrated Crop News. Iowa State University Extension. www.extension.iastate.edu/ (verified 8/22/14); 3 Nafziger, E. 2003. Test weight and yield:
A connection? The Bulletin. University of Illinois. http://bulletin.ipm.illinois.edu/ (verified 8/22/14); 4 Nielsen, R.L. 2012. Test weight issues in corn. Corny News Network. Purdue University.
www.agry.purdue.edu/ext/ (verified 8/22/14).; Bern, C. and T. Brumm. 2009. Grain test weight deception. Iowa State University Extension. PMR 1005. http://lib.dr.iastate.edu/ (verified 8/22/14);
Rankin, M. 2009. Understanding corn test weight. University of Wisconsin Extension. Team Grains.
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