Estimate how many grams of carbohydrate to eat each day from your age, sex, height, weight, and activity. Switch US and metric units, pick Mifflin St Jeor or Katch-McArdle, and see calories plus carb grams at 45%, 55%, 65%, and 75% of intake — including lose- and gain-weight rows.
What are carbohydrates?
Carbohydrates are one of the three energy macronutrients, with protein and fat. They break down to glucose, fuel the brain and working muscles, and can be stored as glycogen or converted to fat. Sugar, starch, and fiber are the usual types: sugar in fruit, dairy, and sweets; starch in grains, beans, and many vegetables; fiber in plants, which supports digestion.
Carbs are not an “essential” nutrient in the strict sense — the body can make glucose — but they are an efficient fuel. Eating them in a sensible range, with an emphasis on fiber-rich foods, is linked in population studies with better cardiovascular and metabolic health than diets built on sugary drinks and refined snacks.
Good carbs and less-helpful carbs
“Good” sources tend to be modest in calories, high in nutrients and natural fiber, and low in refined sugar, sodium, and saturated or trans fat. Think vegetables, whole fruit, beans, and whole grains.
The opposite pattern — calorie-dense, low-fiber, refined flour and added sugars — is easier to overeat. Carbohydrates themselves are not the villain; the package they arrive in matters.
Examples
Man, 25, 5 ft 10 in, 160 lb, light activity
Mifflin St Jeor at light activity (1.375) is 2,361 Calories/day. Carb grams at 45 / 55 / 65 / 75% are 266 / 325 / 384 / 443 g (US also shows ounces and pounds). Lose 1 lb/week is 1,861 Calories; gain 1 lb/week is 2,861.
Woman, 30, 5 ft 4 in, 140 lb, light activity
Female Mifflin at the same activity is 1,843 Calories/day, or 197 / 270 / 319 / 369 g of carbohydrate across the four percentages.
Metric default, 180 cm, 60 kg
The same age-25 male at light activity in metric units is 2,207 Calories/day, 235 / 324 / 383 / 441 g, with kilogram weekly lose/gain labels (0.5 kg and 1 kg per week).
Formula
Calories start with basal metabolic rate (BMR), then an activity factor. Mifflin St Jeor (the default) uses kilograms (W), centimetres (H), and years (A). Katch-McArdle uses lean mass from body-fat fraction (bf):
Men: BMR = 10W + 6.25H − 5A + 5
Women: BMR = 10W + 6.25H − 5A − 161
Katch: BMR = 370 + 21.6 × W × (1 − bf)
Calories = round(BMR × activity)
Carbs g = round(calories × percent ÷ 4)
Goal rows assume about 3,500 calories per pound: 0 (maintain), ±500 (1 lb / 0.5 kg per week), ±1,000 (2 lb / 1 kg). US cells also show ounces and pounds from 1 oz = 28.3495 g and 1 lb = 453.592 g.
| Activity level | Factor |
|---|---|
| Sedentary (little or no exercise) | 1.2 |
| Light (1–3 times/week) | 1.375 |
| Moderate (4–5 times/week) | 1.465 |
| Active (daily, or intense 3–4 times/week) | 1.55 |
| Very Active (intense 6–7 times/week) | 1.725 |
| Extra Active (very intense daily, or physical job) | 1.9 |
Exercise here means 15–30 minutes of elevated heart rate. Intense exercise is 45–120 minutes; very intense is 2+ hours.
These numbers are typical-situation estimates. If you are an athlete, pregnant, or on a medical diet, ask a doctor or registered dietitian before changing how you eat. Very low calorie intakes should only be used under medical supervision.
Sources
- FDA Food Labeling Guide — 4 calories per gram of carbohydrate.
- USDA National Agricultural Library: Macronutrients — National Academies DRI and adult macronutrient ranges.
- Mifflin et al. (1990) — resting-energy equation.