Elemental Calcium Content Converter
Elemental Calcium Content Converter
Convert a calcium salt dose to its elemental calcium content — the figure that dosing guidelines and prescriptions actually specify.
Elemental Calcium Content Converter
Salt → elementalCalcium carbonate 1250 mg (40% elemental)
Formula
- salt dose
- the total weight of the compound as printed on the label, mg
- elemental fraction
- the proportion of that weight which is calcium itself, fixed by the salt's chemistry
Worked example
Calcium carbonate 1250 mg (40% elemental)
1250 × 40 ÷ 100 = 500 mg elemental calcium
Elemental calcium by salt
| Salt | % elemental | 1000 mg salt provides |
|---|---|---|
| Calcium carbonate | 40% | 400 mg |
| Calcium citrate | 21% | 210 mg |
| Calcium lactate | 13% | 130 mg |
| Calcium gluconate | 9.3% | 93 mg |
| Calcium chloride | 27.2% | 272 mg |
Salt dose and elemental dose are not the same number
Supplement labels quote the weight of the salt; prescriptions, dosing guidelines and laboratory advice quote elemental calcium. Confusing the two is a common dosing error in both directions — under-dosing when a clinician assumes the label figure is already elemental, and over-dosing when a patient doubles a supplement without realising the elemental content is much lower than the tablet weight suggests.
Calcium carbonate is 40% elemental calcium and is the cheapest option, but it requires gastric acid for dissolution, so it should be taken with food and is poorly absorbed in a patient on a proton pump inhibitor or with achlorhydria. Calcium citrate is only 21% elemental but absorbs independently of gastric acid, making it the preferred choice in that situation and after bariatric surgery, where acid production and absorptive surface are both reduced.
Absorption efficiency falls once more than about 500 mg of elemental calcium is taken at a single time, so larger daily totals should be divided across two or more doses rather than given as one. For intravenous use the distinction becomes urgent rather than theoretical: 10 mL of 10% calcium gluconate contains about 93 mg (2.3 mmol) of elemental calcium, while the same volume of 10% calcium chloride contains about 272 mg — roughly threefold more — a difference that matters directly in the management of a cardiac arrest with suspected hyperkalaemia or calcium channel blocker toxicity.
Frequently asked questions
How much elemental calcium is in 1000 mg of calcium carbonate?
400 mg. Calcium carbonate is 40% elemental calcium by weight, so 1000 mg of the salt provides 1000 × 0.40 = 400 mg of elemental calcium.
Why is calcium citrate preferred after bariatric surgery?
Calcium citrate absorbs independently of gastric acid, unlike calcium carbonate, which needs acid to dissolve. After bariatric surgery, acid production and absorptive surface area are both reduced, favouring citrate.
Should a large calcium dose be split?
Yes. Absorption efficiency falls once more than about 500 mg of elemental calcium is taken at one time, so daily totals above this should be divided into two or more doses.
What is the difference between IV calcium gluconate and calcium chloride?
10 mL of 10% calcium gluconate provides about 93 mg (2.3 mmol) of elemental calcium, while the same volume of 10% calcium chloride provides about 272 mg — roughly three times as much, which matters in emergency dosing.
Related calculators
References
- Straub DA. Calcium supplementation in clinical practice: a review of forms, doses, and indications. Nutr Clin Pract. 2007;22(3):286–296.
- American Heart Association. Advanced Cardiovascular Life Support: calcium chloride and calcium gluconate in cardiac arrest.