Magnesium Sulfate Dose Calculator
Magnesium sulfate for obstetric use is ordered as a loading dose in grams plus a maintenance dose in grams per hour, but infusion pumps are set in millilitres per hour. This calculator converts both doses into pump rates using the concentration of the bag you have prepared. You enter the loading dose and its infusion time, the maintenance dose, and the grams and volume of the bag; it returns the concentration, the loading-dose rate, and the maintenance rate. It performs arithmetic only. Magnesium sulfate is a high-alert medication, so every order and pump setting must follow your institution's protocol and be independently verified.
Dose-to-rate formula
Concentration (g/mL) = grams in bag / bag volume (mL)
Loading rate (mL/hr) = load (g) / concentration / (load minutes / 60)
Maintenance rate (mL/hr) = maintenance (g/hr) / concentration
Only the 60-minutes-per-hour conversion is a constant; every clinical value remains an editable input that you confirm against your verified order and bag label.
Safe-use context
- Magnesium sulfate is widely classified as a high-alert medication.
- Loading and maintenance regimens vary by indication and protocol.
- Confirm the concentration printed on the prepared bag label.
- Monitor for signs of magnesium toxicity such as loss of reflexes.
- Independent double-checks are standard practice for these infusions.
Magnesium sulfate dose: frequently asked questions
What does this calculator do?
It converts a magnesium sulfate loading dose in grams and a maintenance dose in grams per hour into infusion pump rates in millilitres per hour, using the concentration of your prepared bag. It is a unit-conversion tool and does not recommend any dose.
How is the bag concentration found?
Concentration in grams per millilitre equals the grams of magnesium sulfate in the bag divided by the bag volume in millilitres. For example, 20 g in 500 mL gives 0.04 g/mL, the same as 40 mg/mL.
How is the loading-dose rate calculated?
The pump rate for the loading dose equals the loading dose in grams divided by the concentration in grams per millilitre, divided by the loading time in hours. A 4 g load at 0.04 g/mL over 30 minutes (0.5 hr) is 4 divided by 0.04 divided by 0.5, which is 200 mL/hr.
Why are all the clinical values user inputs?
Magnesium sulfate regimens for preeclampsia, eclampsia, and other indications vary by protocol. To avoid presenting any one regimen as universal, the doses, bag grams, bag volume, and loading time are all editable so the tool reflects your verified order.
Does this replace clinical judgement?
No. Magnesium sulfate is a high-alert medication and overdose can be dangerous. Orders, preparation, pump programming, and monitoring must follow your institution's protocol and be independently verified. This tool performs arithmetic only.
Official sources
- U.S. National Library of Medicine, DailyMed: Drug labelling.
- American College of Obstetricians and Gynecologists: Clinical guidance.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.