1. Intravenous Therapy IV Calculation (Math)
Sasha A. Rarang, RN, MSN

2. Basic Infusion Time Formula
Infusion Time = total volume to infuse
ml/hr being infused
“How long will it take for a particular amount of solution to be completed?”
Ex: Calculate the infusion time for an IV solution of 500 ml D5W that is currently infusing at 50 ml/hr?
500 ml = 10 hrs
50 ml/hr
OR by ratio
50 ml = 500 ml (cross multiply & solve for x)
1 hr x
50x = 500
x = 10 hrs

3. Basic Infusion Time Formula
Time can also be expressed in hours & minutes
Multiply the partial portion (after the decimal point) of the hour by 60 to obtain the time to the nearest minute
Ex: 500 ml = hr
75 ml/hr
.66 x 60 min = 39.6 minutes or 40 minutes
Therefore the TOTAL time is 6.66 hrs or 6 hrs & 40 minutes

4. Flow Rates Refers to an amount of solution over a period of time
Can be expressed as gtt’s/min or ml’s/hr
For our purposes, whenever we discuss regulating an IV by the roller clamp or by gravity, we will use the flow rate of gtt’s/min.
When trying to figure out the flow rate using an IV pump or regulating the IV using a machine, we will use the flow rate of cc’s/hr

5. Flow Rates Flow rate via gravity or by the roller clamp
Refer to your handout “IV Calculation Worksheet”
Vital information needed: microdrip or macrodrip; drop factor

6. IV Drug Amounts
“How much medication is the patient receiving?”
“What is the flow rate to insure proper delivery of the amount of medication ordered?”
D x Q H
Ex: An IV of 1000 ml of D5W containing 40,000 U of Heparin is ordered to infuse at 30 ml/hr. Calculate the dosage of Heparin the pt is receiving (How many units/hr of Heparin)
30ml/hr x 40,000 u = u/hr
1000 ml
OR by ratio ,000 u = x u (cross multiply & solve for x)
1,000 ml ml
1,000x =
x = u/hr

7. IV Drug Amounts
Ex: Morphine Sulfate IV drip concentration 50 mg in 100 cc D5W. MD orders 2mg of Morphine per hour. What will the flow rate be to insure delivery of 2 mg/hr? ( How many cc’s per hr?)
2mg/hr x cc = cc/hr
50 mg
Or by ratio mg = mg (cross multiply & solve for x)
100 cc x cc
50 x =
x = cc/hr