Methodology

Last updated: September 6, 2026

The calculator formula

Two methods, both from the Institute of Medicine’s Dietary Reference Intakes:

• Age and sex table (the default): the IOM Adequate Intake values. 25 g per day for women and 38 g for men aged 19 to 50; 21 g and 30 g after 50; 28 g in pregnancy; 29 g when breastfeeding; age-banded values for children.
• Energy method (when you enter calories): 14 g per 1,000 kcal consumed, the basis the IOM used to derive the table. It’s the more precise method because fiber needs track energy intake, and it’s what the weight loss variant applies to goal calories.

We also always show the FDA Daily Value (28 g) alongside your personal target, because that’s the reference behind the “% DV” on food labels. Two different numbers, both correct, used for different things.

Food data

Serving values are USDA data (SR Legacy household servings) as published in standard clinical fiber tables, and are checked against USDA FoodData Central releases on a regular refresh schedule.

Where sources disagree, we say so. Example: USDA’s newer Foundation analysis measures a medium Fuji apple at about 3.8 g of fiber while the widely cited legacy value is 4.4 g. Different apple varieties, different lab methods. When a number has this kind of spread, the page notes it rather than silently picking one.

The soluble and insoluble split

USDA FoodData Central tracks total fiber only; no official soluble/insoluble split exists. Our split table is hand-compiled from peer-reviewed analyses (Anderson & Bridges 1988; Marlett 1992; Li, Andrews & Pehrsson 2002). Values are cross-checked where studies overlap, and the table grows as each new row is verified against its citation. Slower than scraping, which is the point.

Corrections

Every figure should trace to a source on the sources page. If one doesn’t, or looks wrong, contact us. Verified corrections ship in the next update.