Thousand Seed Weight Calculators

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Thousand seed weight (TSW) is the weight in grams of exactly 1,000 seeds of a crop variety or seed lot. It determines the number of seeds per kilogram (seeds/kg = 1,000,000 / TSW) and is a critical input for calculating seeding rates. TSW varies considerably between species (wheat ~40–55 g; maize ~250–350 g; canola ~3–5 g), between varieties of the same species, and between different seed lots of the same variety due to growing conditions. TSW is always measured on the specific seed lot to be used — never estimated from general values — and is printed on commercial seed bags along with germination percentage.

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TSW Measurement Protocol

Count out exactly 1,000 seeds manually or using an electronic seed counter. Weigh on an analytical balance to the nearest 0.1 g. Repeat with a second set of 1,000 seeds. Average the two weights = TSW. If the difference between the two counts exceeds 5%: repeat.

TSW and Sowing Rate

Seeds per kg = 1,000,000 / TSW. Sowing rate (kg/ha) = (target plants/m² × TSW × 100) / (germination% × establishment%). Example: maize with TSW = 300 g; target 8 plants/m²; germination 95%; establishment 92%: kg/ha = (8 × 300 × 100) / (95 × 92) = 240,000 / 8,740 = 27.5 kg/ha.

Typical TSW Values

  • Wheat: 35–55 g (average ~45 g)
  • Maize: 250–350 g
  • Soybean: 150–250 g
  • Canola/OSR: 3–5 g
  • Sugar beet (monogerm): 15–20 g
  • Lettuce: 0.8–1.2 g
  • Sunflower: 40–80 g

TSW and Seed Quality

Larger seeds (higher TSW) generally have more endosperm reserves → better seedling establishment. TSW correlates weakly with germination% — both must be measured independently. Variation in TSW of ±20–30% within a species is common between growing seasons and varieties.

Glossary

Thousand Seed Weight (TSW)
Weight (g) of exactly 1,000 seeds; determines seeds/kg = 1,000,000/TSW; printed on commercial seed bags; varies ±20–30% between lots; must be measured on the actual lot used.
Seeds per Kilogram
1,000,000 / TSW (g); determines how many seeds are in a kilogram of a seed lot; used with target plant density to calculate sowing rate in kg/ha.
Sowing Rate
(Target plants/m² × TSW × 100) / (germination% × establishment%); the kg of seed to sow per hectare; always calculated using the actual TSW and germination% of the specific lot.

Frequently Asked Questions

Thousand seed weight (TSW) = weight in grams of exactly 1,000 seeds. Measurement: count exactly 1,000 seeds (by hand or electronic counter); weigh on a balance (±0.1 g); repeat with a second set; average. If the two weights differ by > 5%: discard and remeasure. The TSW for that specific seed lot is then used in sowing rate calculations. Printed on commercial seed bags alongside germination% and purity. TSW must always be measured on the actual lot being planted — never estimated from variety averages, because seed size varies by ±20–30% between lots.

Seeds per kg = 1,000,000 / TSW (g). Examples: Canola (TSW = 4 g): 1,000,000/4 = 250,000 seeds/kg. Wheat (TSW = 45 g): 1,000,000/45 = 22,222 seeds/kg. Maize (TSW = 300 g): 1,000,000/300 = 3,333 seeds/kg. This is why crops with low TSW (canola) have very high seeds per kg and require very low sowing rates in kg/ha, while crops with high TSW (maize, soybean) have fewer seeds per kg. The seeds/kg value directly affects how many kilograms must be purchased for a given target seeding rate.

TSW is a proxy for seed reserves (mainly endosperm energy and nutrients): Higher TSW seeds: more energy reserves for the emerging seedling; better emergence through deeper soil or crusted soils; more robust seedlings under early-season stress (drought, cold). But TSW and germination% are not closely correlated — a large seed may have poor germination (immature, damaged, or diseased) and a small seed may have excellent germination. Both TSW and germination% must be measured independently. Large-seeded varieties generally give more reliable establishment under suboptimal seedbed conditions, which is why higher TSW is often selected for in breeding programs targeting reliability.

TSW varies between seed lots by ±20–30% for the same crop variety. Effect on sowing rate: if TSW is 10% higher than average, you need 10% more kg/ha of seed (same number of seeds per kg means fewer seeds per kg). Example: wheat target population 300 plants/m²; germination 94%; establishment 90%. At TSW = 40 g: sowing rate = (300 × 40 × 100)/(94 × 90) = 141 kg/ha. At TSW = 50 g (25% higher): sowing rate = (300 × 50 × 100)/(94 × 90) = 176 kg/ha — 25% more seed required for the same target population. Failing to account for actual TSW can result in significant under- or over-seeding.