As harvest approaches, many producers across Central Illinois are asking the same question: How’s the crop looking? Estimating corn and soybean yields before the combine rolls is more than just curiosity—it’s a valuable tool for planning, marketing, and managing risk. While yield estimates aren’t perfect, they offer a snapshot of field performance and help guide decisions on storage, sales, and insurance. This post will walk through practical, field-tested methods for estimating corn and soybean yields using simple tools and observations. Whether scouting a few acres or evaluating whole fields, these techniques can help turn plant counts, ear sizes, and pod numbers into meaningful yield projections. With a bit of math and a sharp eye, producers can gain insights into their crop’s potential and make more informed decisions this season.
Estimating Corn Yield
While there are various methods for estimating corn yield, the most proven method used by producers and others is the Yield Component Method. Developed at the University of Illinois, it is popular because it can be done as early as the R3 “milk” stage.
Step 1: Pick a Reference Point
The first step is selecting a spot in the field to serve as a reference point, ideally located in the “bulk” of the field. Once that reference point is established, the next step is marking off 1/1,000 of an acre. To do this, use the following equation:
Length = (43,560/row spacing in feet)/1,000.
Let’s say the field has 30-inch rows, common across the Midwest. Divide 43,560 by 2.5 (which is 30 inches in feet), then divide that result by 1,000. This gives roughly 17 feet, 5 inches, and would be the required length for the sample. The required lengths for other row spacings are:
- 15 inches - 34 feet, 10 inches
- 20 inches - 26 feet, 2 inches
- 22 inches - 23 feet, 9 inches
- 36 inches - 14 feet, 6 inches
- 38 inches - 13 feet, 9 inches
Step 2: Counting Ears
The second step is counting the number of ears in a 1/1,000-acre row. It’s important to only count those ears that a harvester can pick up. This means any lodged plants or ears that have fallen off should not be counted.
Step 3: Picking Ears
The third step is selecting ears in the sample area. At least three ears should be selected, but more can be picked to improve accuracy. Try to avoid choosing ears that are stunted or have issues, unless they are representative of the area being sampled.
Step 4: Kernels in Selected Ears
The fourth step involves calculating the average number of kernels per ear based on the ears selected in step three. To do this, count the number of kernel rows on each ear and the kernels in a row. Do not count aborted kernels or kernels on the extreme ends of the ear. Multiply the number of rows by the number of kernels per row to find the number of kernels per ear at a sample point.
Step 5: Kernels per Ear
The fifth step is calculating the average number of kernels per ear in the sample area. For each ear where kernel numbers were calculated, add all the counts together and then divide by the number of ears. For example, if you calculated kernel counts on five ears with 480, 500, 450, 600, and 525 kernels respectively, add those numbers and divide by five (2,555/5) to get an average of 511 kernels per ear in the sample area.
Step 6: Calculate Yield
The final step is to estimate yield. This involves multiplying the number of harvestable ears in the sample area by the average kernels per ear, then dividing by kernel weight. For example, if there are 30 ears in the sample with an average of 511 kernels per ear, you'd use this data. To account for different kernel sizes, a common practice is to use four values: 65, 75, 85, and 95. Calculate yields with each value to determine an estimated range. The results are:
- (30 x 511) 65 = 235.84 bushels per acre
- (30 x 511) 75 = 204.4 bushels per acre
- (30 x 511) 85 = 180.35 bushels per acre
- (30 x 511) 95 = 161. 26 bushels per acre
Estimating Soybean Yield
The process for estimating soybean yield is similar to estimating corn yield, but it can be less accurate due to variability from plant to plant. To improve accuracy, estimate yields later in the growing season, especially when the plant reaches the R6 “full seed” stage.
Step 1: Estimate Plant Population
The method for estimating soybean yield also starts with estimating plant population. One way to do it is the “hula hoop” method by tossing a hula hoop at five random areas of a field and counting the number of plants in the hula hoop. Average the number of plants from each location, then multiply that by the conversion factor based on the diameter of the hula hoop from this list:
- 18 inches - 24,662
- 21 inches - 18,119
- 24 inches - 13,872
- 27 inches - 10,961
- 30 inches - 8,878
- 33 inches - 7,337
- 36 inches - 6,165
Let’s say there is an average of 13.5 plants across each location using a 30-inch hula hoop. Using the conversion factor (13.5 x 8,878) gives an estimated plant population of 120,000.
Step 2: Pods per Plant
The next step is to randomly select ten plants and count the number of pods on those plants. Then, calculate the average number of pods in those ten plants. Let’s use an average of 25 pods per plant for our example.
Step 3: Additional Information
Additional information is needed to estimate yield. The average number of seeds per pod is normally 2.5, but this can be adjusted depending on weather and pest pressures. Similarly, there are 3,000 seeds per pound, which can be adjusted based on pressure.
Step 4: Calculate Yield
With this information, we can then use the equation for calculating yield:
Bushels per acre = (Population) x (Pods per plant) x (Seeds per pod) ÷ (Seeds per pound) ÷ (60 pounds per bushel)
Let’s use the information we have listed above and plug that into the equation. 120,000 x 30 x 2.5 ÷ 3,000 ÷ 60 is roughly 50 bushels per acre.
Estimating corn and soybean yields before harvest is a valuable practice that helps producers make informed decisions about marketing, storage, and risk management. While no method is perfect, using simple tools like the hula hoop and a few calculations can provide a reliable snapshot of your crop’s potential. Whether you're scouting a few fields or preparing for harvest across your operation, yield estimates offer insight that’s worth the effort. If you have questions about these methods or want help interpreting your results, don’t hesitate to reach out to your local Extension office—we’re here to support your success this season.
For further reading, visit the following links:
- Estimating Corn Yield
- Corn Yield Estimates (Iowa State University Extension, 2020)
- Estimating Corn Grain Yields (Penn State University Extension, 2023)
- Estimating Corn Grain Yield Prior to Harvest (Purdue University Extension, 2021)
- Estimating Soybean Yield
- Assessing Soybean Stands (Michigan State University Extension, 2024)
- Estimating Soybean Yield (Ohio State University Extension, 2018)
- Soybean Yield Estimates (Iowa State University Extension, 2020)