Grams, kilograms, ml, cc; what does it all mean? What cattleman hasn’t stood with medication in hand and wondered if he was helping or making things worse with a wrong dosage. It really isn’t complicated, but it may seem that way to livestock producers who don’t use these applications in everyday life. Let’s shed some light on the subject.

The basic unit of volume in the metric system is the liter (L), which is slightly larger than a quart (qt) – 1.06 times the volume of a quart to be exact. Liters are commonly divided into milliliters, abbreviated mL. Each milliliter is equal in volume to a cube which is one centimeter wide, one centimeter long, and one centimeter high. Thus 1 mL and 1 cubic centimeter (cc) express the same unit of volume and can be used interchangeably. There are 30 cc or mL in 1 fluid ounce. As every housewife knows, there are 6 teaspoons or 2 tablespoons in a fluid ounce, so there are 5 cc or mL in a teaspoon, or 15 cc or mL in a tablespoon.

Volume conversions
U.S. Metric
1 cup = 8 fl oz 1 ml = 1cc
1 pint = 16 fl oz 1,000 ml = 1 liter
1 qt = 32 fl oz 1,000 cc = 1 liter
1 fl oz = 30 cc
1 qt = 0.95 liters
1.06 qt = 1 liter
1 teaspoon = 5 cc
1 tablespoon = 15 cc

The basic unit of weight in the metric system is the gram (g). One g is defined as the weight of water that occupies 1 cc at the temperature at which ice starts to melt. There are 454 g in 1 pound (lb.), and 1,000 g equals 1 kilogram (kg), which is equal to 2.2 lbs. One thousandth of a gram equals 1 milligram (mg). Thus, there are about 31 g or 31,000 mg in 1 oz.

Weight conversions
1,000 grams = 1 kilogram
1,000 milligrams = 1 gram
2.2 lb = 1 kilogram
1 lb = .45 kilogram
1 lb = 454 grams
1 oz = 31.1 grams

Appropriate dosages of pharmaceuticals are often expressed in grams or milligrams per unit of body weight of the animal to be dosed. When medications are given, they’re commonly measured in units of volume such as cc or fluid ounces. To determine the correct dose for an individual animal, you must know the concentration, which is the amount of the drug expressed in units of weight that will be present in each unit of volume of the product.

For example, an antibiotic is packaged and distributed at a concentration of 200 mg/mL. The recommended dose is 9 mg/lb. of bodyweight. How many cc would you give a 120-lb. calf? 120 lbs. times the 9 mg required for 1 lb. of bodyweight equals 1,080 mg required. Since we know the product’s concentration is 200 mg/mL, we can divide 200 into the requirement of 1,080 and find we need 5.4 mL or 5.4 cc.

Dosages for oral medications are often expressed in fluid ounces rather than mL or cc. The same principles apply in that we need to know the amount of the drug required and the concentration of the product as supplied.

Most over-the-counter drugs have dosing guidelines very easy to interpret. Prescription drugs, however, may express the dosing guidelines in terms not so familiar, and drugs for off-label usage will have no guidelines for that application, other than what your veterinarian provides. It may be helpful to know that a dosage level of 1 mg/kg of bodyweight is equal to 46 mg/100 lbs. of bodyweight. If dosage is expressed in units of volume, you can remember that 1 mL or cc/kg of bodyweight equals .46 mL or cc/lb. of bodyweight.

Dosage conversions
1 mg/kg BW = .46 mg/lb BW
1 mg/kg BW = 46 mg/100 lb BW
1cc/kg BW = .46 cc/lb BW

Although we’re blessed today with many effective drugs to safeguard the health of our livestock, minor errors in dosage can result in major problems. Always follow the label directions carefully. If you aren’t clear on what or how much to use, or how best to administer the drug, always consult your local veterinarian.

In many countries, producers aren’t allowed to self administer drugs to their livestock. The future of our ability to medicate our livestock depends the job we do of using drugs responsibly today.
-- Dave Sparks DVM, Oklahoma State University