Soy foods are some of the most iron-rich plant proteins available, but the amount of iron varies dramatically from product to product. A cup of soy milk delivers only a trace, while firm tofu and dry roasted soybeans pack several milligrams per serving. This Soy Iron Calculator lets you quickly estimate the iron content of the soy foods you actually eat — whether you’re tracking a daily goal, meal planning for a vegetarian or vegan diet, or comparing products at the grocery store.
Just choose a soy product, enter the serving size in grams or ounces, and pick a daily iron target that matches your life stage. The calculator returns milligrams of iron, its percentage of the FDA Daily Value, and a share of your personal target. It also shows the simple math behind each estimate so you can understand how the numbers are derived. All values are based on standard USDA FoodData Central reference data. Because soy contains non-heme iron, you’ll also find practical tips on absorption in the sections below.
📊 Iron result
Why Soy Iron Matters
Iron is essential for oxygen transport, energy production, and immune function, and it is one of the nutrients most commonly missing from plant-forward diets. Soy foods offer a practical plant-based iron source, but their iron content varies widely. Firm tofu, natto, and dry roasted soybeans are concentrated sources, while soy milk and miso contribute smaller amounts per serving. For vegetarians, vegans, athletes, and anyone trying to increase dietary iron without relying on red meat, understanding the iron difference between soy products makes meal planning easier. Instead of assuming all soy is high in iron, you can target the foods that actually move the needle toward your daily goal.
Soy Iron at a Glance
The table below shows average iron values per 100 g of each product, along with a common serving size and the iron that serving provides. Values are compiled from USDA FoodData Central and rounded for everyday use.
| Product | Iron per 100 g | Common portion | Iron per portion |
|---|---|---|---|
| Firm tofu | 5.36 mg | 1/2 cup (126 g) | 6.75 mg |
| Dry roasted soybeans | 6.47 mg | 1 oz (28 g) | 1.81 mg |
| Natto | 6.50 mg | 1 small pack (50 g) | 3.25 mg |
| Soft tofu | 3.35 mg | 1/2 cup (126 g) | 4.22 mg |
| Edamame, cooked | 2.79 mg | 1/2 cup (75 g) | 2.09 mg |
| Tempeh | 2.70 mg | 1/2 cup (83 g) | 2.24 mg |
| Miso | 2.49 mg | 1 tbsp (18 g) | 0.45 mg |
| Soy milk, unsweetened | 0.42 mg | 1 cup (240 g) | 1.01 mg |
How to Use This Calculator
- Choose the soy product that matches what you are eating.
- Enter the serving size in grams or ounces — a kitchen scale gives the most accurate number.
- Select the daily iron goal that applies to you, or keep the FDA 18 mg Daily Value.
- Click Calculate iron to see milligrams of iron, percent of Daily Value, and percent of your personal target.
The result box also shows the calculation steps, so you can check the math or adapt it to a different serving size.
How the Iron Values Are Calculated
Each product has a reference value: milligrams of iron per 100 g of food. To estimate your serving, the calculator converts ounces to grams, then applies this formula:
For example, if you eat 85 g of firm tofu (5.36 mg/100 g), the estimate is 85 ÷ 100 × 5.36 = 4.56 mg. The calculator uses the reference values in the table above. These figures are typical averages from USDA FoodData Central, but actual iron can vary with brand, processing method, fortification, and how the food is prepared. Use them as planning estimates rather than lab-precise numbers.
Worked Examples
Example 1: Firm tofu bowl. 126 g firm tofu → 126 ÷ 100 × 5.36 = 6.75 mg iron. This covers about 38% of an 18 mg Daily Value.
Example 2: Edamame snack. 75 g cooked edamame → 75 ÷ 100 × 2.79 = 2.09 mg iron.
Example 3: Soy milk smoothie. 240 g unsweetened soy milk → 240 ÷ 100 × 0.42 = 1.01 mg iron.
Notice how the same gram weight can produce very different amounts. Choosing a concentrated soy food like tofu, natto, or roasted soybeans makes a much larger contribution to your iron target than choosing a diluted product like soy milk.
Absorption, Limitations & FAQs
Soy iron is non-heme iron, which the body absorbs less efficiently than the heme iron found in meat. Estimated absorption of non-heme iron is roughly 2–20% depending on your iron stores and the meal composition. Soy also contains phytates, natural compounds that can bind iron and reduce absorption.
Frequently asked questions