One serving against a day's fiber
The Dietary Reference Intakes set an Adequate Intake for total fiber of 25 g a day for women aged 19 to 50 and 38 g for men of the same ages. Measured against those, the 9.8 g in a 2 tbsp serving of chia seeds is 39% of the first and 26% of the second. US food labels use a single Daily Value of 28 g instead, which puts this serving at 35%.
Calorie for calorie, the figure is 7.1 g of fiber per 100 kcal. Among the 14 seeds with USDA energy data here that is 1st, and 59th across all 957. The intakes above were derived from 14 g of fiber per 1,000 kcal, or 1.4 g per 100 kcal, so this food sits above the ratio a whole day of eating is meant to reach.
Getting all 25 g from chia seeds alone would take 3 servings, and 38 g would take 4. Most days reach the target through several different sources.
Soluble vs Insoluble Fiber: What Each One Actually Does · All fiber guides