Crunching Numbers Simplified for Equine Nutrition

by Juliet M. Getty, Ph.D.

Have you ever looked at a hay analysis or feed tag and thought, What does this actually mean for my horse? You’re not alone. Numbers like “ppm” and percentages can seem confusing—but once you understand a couple of simple conversions, everything becomes much clearer.

And that clarity matters. When it comes to nutrients like selenium, copper, or magnesium, small differences can have a big impact on your horse’s health.

What does “ppm” really mean?

You’ll often see nutrients listed as ppm (parts per million). That may sound technical, but it’s actually quite simple:

ppm = milligrams per kilogram (mg/kg)

So instead of overthinking it, just read ppm as mg/kg.

The only trick? You need your feed amount in kilograms, not pounds or ounces. 

Example: Selenium in hay

Let’s say your hay contains 0.2 ppm selenium and your horse eats 20 lbs of hay.

Step 1: Convert pounds to kilograms
20 lbs × 0.454 = 9.08 kg

Step 2: Multiply by ppm
9.08 × 0.2 = 1.816 mg selenium

Now you know exactly how much selenium your horse is getting from that hay.

Example: Copper in a supplement

Your supplement contains 150 ppm copper per ounce.

Step 1: Convert ounces to kilograms
1 ounce = 28.35 grams
28.35 ÷ 1000 = 0.02835 kg

Step 2: Multiply by ppm
0.02835 × 150 = 4.25 mg copper

Quick ppm formulas

  • Pounds → kilograms:
    lbs × 0.454 = kg
  • Ounces → kilograms:
    oz × 28.35 ÷ 1000 = kg
  • Find milligrams:
    kg × ppm = mg

What about percentages?

Some nutrients are listed as percentages instead of ppm—typically those present in larger amounts, like:

  • Crude protein
  • Sugars (ESC, WSC)
  • Major minerals (calcium, phosphorus, magnesium)

A percentage simply means “per 100.”
So 8% protein = 8 grams per 100 grams of feed.

Example: Protein in hay

Your hay is 8% crude protein, and your horse eats 20 lbs.

Step 1: Convert to grams
20 lbs × 454 = 9080 grams

Step 2: Multiply by percentage
9080 × 0.08 = 726.4 grams of protein

Example: Magnesium in hay

Your hay contains 0.07% magnesium.

Step 1: Convert to grams
20 lbs × 454 = 9080 grams

Step 2: Multiply by percentage
9080 × 0.0007 = 6.36 grams magnesium
(or 6,360 mg)

Quick percentage formulas

  • Pounds → grams:
    lbs × 454 = grams
  • Find grams:
    grams × percentage = grams

Bottom line

Whether a nutrient is listed as ppm or a percentage, both simply describe concentration. With a few easy conversions, you can translate those numbers into something meaningful—exactly how much of a nutrient your horse is actually consuming.

And once you can do that, you’re no longer guessing—you’re making informed, precise feeding decisions.

For Permission to Reprint

For permission to reprint this article, in part or in its entirety, or arrange for a private consultation, please contact Dr. Getty directly at gettyequinenutrition@gmail.com.