Egg shells are one of the most calcium-dense natural materials you’ll find in a kitchen. A single chicken eggshell is about 94% calcium carbonate by weight, delivering roughly 380 milligrams of elemental calcium per gram of shell. That means one large eggshell, ground into powder, contains nearly twice the calcium in a glass of milk.
What’s Actually in an Eggshell
Calcium carbonate makes up the overwhelming majority of an eggshell’s structure, sometimes measured as high as 96% by weight. The remaining fraction includes about 1% magnesium carbonate, 1% calcium phosphate, and 4% organic matter (the proteins that form the shell’s framework). Trace amounts of sodium, potassium, sulfur, phosphorus, copper, and iron round out the profile, though none of these are present in nutritionally meaningful quantities.
The calcium itself is the same chemical form found in many over-the-counter supplements: calcium carbonate. Gram for gram, eggshell powder contains 360 to 400 milligrams of elemental calcium, averaging about 378 mg per gram. Half a teaspoon of finely ground eggshell powder is roughly one gram, which puts it in the range of a standard calcium supplement tablet.
How It Compares to Supplements
Because eggshell calcium is chemically identical to the calcium carbonate in most store-bought supplements, your body absorbs it the same way. Calcium carbonate is best absorbed when taken with food, since stomach acid helps break it down. If you’ve used a calcium carbonate supplement before, eggshell powder behaves similarly in your digestive system.
A clinical trial in the Netherlands tested a supplement enriched with chicken eggshell powder in postmenopausal women. After 12 months, women taking the eggshell-based supplement saw a 1.75% increase in bone mineral density at the hip, while the control group experienced a slight decrease. That’s a modest but meaningful difference, particularly for a population at elevated risk for fractures.
Digestive Effects
One common concern with calcium carbonate supplements is constipation or stomach upset. A six-month trial in Ethiopia, where women took eggshell powder daily, found no increase in constipation or bloating compared to the control group. The supplemented group actually reported fewer symptoms of nausea and loss of appetite over time. This suggests eggshell calcium is at least as well tolerated as standard supplements, and possibly gentler for some people.
Making Eggshell Powder Safely
Raw eggshells can carry Salmonella and E. coli, so proper cleaning and heat treatment are essential before you grind them into anything edible. Research on sterilization found two effective methods: boiling shells in water at 95°C (just below a rolling boil) for a full 60 minutes, or steaming them at 121°C for 15 minutes. Both approaches eliminated Salmonella entirely and reduced bacterial counts to negligible levels. A quick 10-minute boil is not enough to guarantee safety.
After sterilizing, dry the shells completely in an oven at a low temperature (around 90 to 100°C works well) until they’re brittle. Then grind them as finely as possible. Studies that tested calcium dissolution used particles between 90 and 125 micrometers in diameter, roughly the texture of fine flour. A coffee grinder or spice grinder can achieve this, but you’ll want to sift the result and re-grind any larger pieces. Coarse fragments won’t dissolve well in your stomach and can feel gritty in food.
How Much to Use
Since one gram of eggshell powder provides about 380 mg of calcium, and most adults need 1,000 to 1,200 mg of calcium daily from all sources combined, a half teaspoon mixed into a smoothie, oatmeal, or soup can meaningfully close a dietary gap. There’s no benefit to exceeding 500 mg of calcium in a single sitting, since your body’s absorption efficiency drops sharply above that amount. Splitting your intake across meals gives you more usable calcium from the same amount of powder.
Keep in mind that you’re likely already getting calcium from dairy, leafy greens, fortified foods, or other sources throughout the day. The goal is to fill a gap, not to maximize intake. Too much calcium from any source, including eggshells, can contribute to kidney stones in susceptible individuals.
Who Benefits Most
Eggshell powder is most practical for people in two situations: those who want a low-cost calcium source and those who prefer a whole-food alternative to commercial supplements. In sub-Saharan Africa, where dairy products and supplements can be expensive or unavailable, researchers have specifically studied eggshell powder as a way to improve calcium intake in pregnant women and children. The World Health Organization recommends 1.5 to 2.0 grams of supplemental calcium daily for pregnant women with low dietary intake, and eggshell powder can realistically meet that need at virtually no cost.
For people in wealthier countries with access to affordable supplements, the practical advantage is smaller. But if you eat eggs regularly and dislike swallowing pills, repurposing the shells is a legitimate option, provided you’re thorough about sterilization and grinding.