Using Thousand Kernel Weight (TKW) to Dial in Wheat Seeding Rates

When it comes to targeted seeding rates, pounds per acre or bushels per acre can be misleading. What we’re really trying to achieve is plants per square foot , which ultimately drives yield, and the best way to get there is by using Thousand Kernel Weight (TKW).

The photo below shows a clear example of why this matters. Irrigated wheat and dryland wheat — and different varieties — all show noticeably different kernel sizes.

The measured TKW values are:

• Alotta wheat (irrigated): 50.6 g

• Irrigation wheat lot #1: 44 g

• Irrigation wheat lot #2: 39.7 g

• Dryland wheat: 34.8 g

That’s a 45% swing in seed size from smallest to largest. If all of these were seeded at the same pounds per acre, they would not produce the same plant population. (Oh and how about that Alotta wheat - hey?! This is a great variety - for more information see this link - Alotta Wheat)

Let’s Work Through an Example

Step 1: Start With a Plant Population Target

On our farm, we typically target:

• Dryland wheat: ~25 plants per square foot

• Irrigated wheat: ~33 plants per square foot

Many factors can shift this rate, including moisture conditions, seeding date, and frost risk.

For this example, let’s assume:

• Target = 25 plants per square foot

• 95% emergence (98% germination minus 3% estimated seedling loss)

Step 2: Convert Target Plants per Square Foot to Seeds per Acre

There are 43,560 square feet in an acre.

25 plants/ft² × 43,560 = 1,089,000 plants per acre

Adjusting for 95% emergence:

1,089,000 ÷ 0.95 = 1,146,316 seeds per acre

So regardless of seed size, we need about 1.15 million seeds per acre to hit 25 plants per square foot.

Step 3: Convert TKW to Pounds per Acre

TKW tells us how much 1,000 seeds weigh in grams. That weight determines how many pounds of seed are required per acre to reach our target population.

Example 1: TKW = 34.8 g

1,146,316 ÷ 1,000 = 1,146 thousand-seed units
1,146 × 34.8 g = 39,880 g
39,880 g ÷ 454 g/lb = 88 lb/ac

Example 2: TKW = 44 g

1,146 × 44 g = 50,424 g
50,424 g ÷ 454 = 111 lb/ac

Example 3: TKW = 50.6 g

1,146 × 50.6 g = 58,008 g
58,008 g ÷ 454 = 128 lb/ac

The Big Takeaway

To hit the same plant population (25 plants/ft²):

• 34.8 g TKW → 88 lb/ac

• 44 g TKW → 111 lb/ac

• 50.6 g TKW → 128 lb/ac

That’s a 40 lb/ac difference driven entirely by seed size.

If all three lots were seeded at 100 lb/ac:

• The small-seeded lot would be overpopulated.

• The large-seeded lot would be underpopulated.

Same crop. Same germination. Very different stand.

Practical Recommendation

We hope that example put tkw into perspective when you are planning your seeding rates this spring.
 

Oh, and don't forget to check out our seed for sale this spring: