Energy-Corrected Milk (ECM) & Fat-Corrected Milk (FCM) Calculator
Convert a cow’s daily milk, fat % and protein % into energy-corrected milk (ECM) and 4% or 3.5% fat-corrected milk (FCM), and get feed efficiency (ECM ÷ dry matter intake).
How it works
ECM = 0.327 × milk + 12.95 × fat yield + 7.2 × protein yield · 4% FCM = 0.4 × milk + 15 × fat yield · 3.5% FCM = 0.4324 × milk + 16.216 × fat yield · Feed efficiency = ECM ÷ dry matter intake (all in the same mass unit per day)
Milk with more fat and protein carries more energy, so comparing cows, herds or diets on raw litres is misleading. Energy-corrected milk standardises every cow to milk with 3.5% fat and 3.2% protein (the Tyrrell & Reid-based equation used by DHI), while the older Gaines formula corrects for fat only, to 4%. Dividing ECM by dry matter intake gives feed efficiency: about 1.4–1.6 for most lactating herds, higher in early lactation and lower in late lactation.
Worked example
A cow giving 30 kg of milk with 3.8% fat and 3.2% protein produces 1.14 kg of fat and 0.96 kg of protein. ECM = 0.327 × 30 + 12.95 × 1.14 + 7.2 × 0.96 = 9.81 + 14.76 + 6.91 = 31.5 kg/day. 4% FCM = 0.4 × 30 + 15 × 1.14 = 29.1 kg/day. Eating 22 kg of dry matter, her feed efficiency is 31.5 ÷ 22 = 1.43 — "Good".
Sources: Hall (2023) — Invited review: Corrected milk: reconsideration of common equations, Journal of Dairy Science · DNMC — Energy corrected milk: which equation are you using?
Frequently asked questions
What is the difference between ECM and FCM?
Fat-corrected milk (FCM) adjusts only for fat content, usually to 4% or 3.5%. Energy-corrected milk (ECM) adjusts for both fat and protein, so it reflects the energy and the value of the milk more fully and is the standard for feed-efficiency comparisons.
What is a good feed efficiency for dairy cows?
Most lactating herds achieve 1.4–1.6 kg of ECM per kg of dry matter. Fresh and early-lactation cows can exceed 1.6, while late-lactation cows and first-calf heifers are often 1.2–1.4. Below about 1.3 is worth investigating in a mature, mid-lactation group.
Can I use litres instead of kilograms?
Milk weighs about 1.03 kg per litre, so litres give an ECM about 3% too low. Multiply litres by 1.03 first if you need an exact figure.
Why is my ECM higher than my actual milk?
Because your milk is richer than the 3.5% fat and 3.2% protein reference. Jersey and other high-component cows often produce ECM 15–25% above their actual milk volume.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.