FCR in broilers — how to calculate (formula and Ross 308 norms)
FCR — feed conversion ratio — tells you how many kilograms of feed were needed for every kilogram of live weight the flock produced. The lower the FCR, the cheaper the rearing cycle. We explain the formula in plain language, show a worked example, and give indicative norms from Ross 308.
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FCR (Feed Conversion Ratio) is one of the key numbers in broiler production. It tells you how many kilograms of feed the flock consumed for every kilogram of live weight produced in that cycle. You do not need any software — you can work it out on a piece of paper. This page is part of the broiler cluster — the full production picture is in the guide on broiler farming.
Why does FCR matter?
Feed typically accounts for 60–70% of total broiler production cost. A difference of 0.10 in FCR (e.g. 1.53 instead of 1.63) on a flock of 20,000 birds means hundreds of kilograms of feed saved per cycle. That is why farmers and advisors track FCR every cycle and compare it with the norms for their genetic line. FCR connects to other performance indicators — including EPEF and feed cost per kg of live weight.
Where do the numbers in this guide come from?
Indicative norms are from Aviagen — Ross 308 Performance Objectives 2022 (aviagen.com). They may differ depending on genetic line, feeding programme, farm conditions, and country. Treat them as reference points, not guarantees. Feeding details and nutrient norms are covered in a separate guide: broiler nutrition — norms.
How to calculate FCR — a step-by-step example with real numbers
- 1
Collect the data: how much feed the flock consumed and how much live weight it produced
To calculate FCR you need two numbers: (1) total feed consumed in the cycle — in kilograms; (2) total live weight collected from the flock — in kilograms (the live weight of the birds on the day of collection). Example: the flock consumed 4,590 kg of feed. At collection the birds were weighed — 3,000 kg of live weight in total.
- 2
Apply the formula: FCR = feed consumed (kg) ÷ live weight (kg)
Read the formula like this: divide the total amount of feed eaten by the flock by the total live weight collected from the flock. The result is the FCR — how many kilograms of feed were used for every kilogram of live weight produced. Example: FCR = 4,590 kg ÷ 3,000 kg = 1.53. That means 1.53 kg of feed went into every 1 kg of live weight.
- 3
Interpret the result: the lower the FCR, the better
FCR is always greater than 1 (no bird weighs more than it has eaten). A good result is the lowest possible value. FCR = 1.53 indicates efficient production. FCR = 1.80 or above is a signal that something is wrong — disease, poor feed, management errors. In our example: FCR 1.53 for a flock collected around day 42 is close to the indicative norm from Ross 308.
- 4
Compare with the norm and with the previous cycle
An FCR figure has the most value when you compare it with two things: (1) the indicative norm for your genetic line (e.g. Ross 308) and (2) the result from the previous cycle in the same house. If FCR is rising cycle after cycle without changes in stocking or feeding, look for the cause — litter moisture, flock health, feed quality. Comparing cycle results is easy with a digital flock record.
FCR in broilers according to Ross 308 — indicative values
Indicative FCR norms for different collection days according to Ross 308 Performance Objectives 2022*. Actual results depend on genetic line, feeding programme, and farm conditions.
Day 35 — FCR approx. 1.40
At around 35 days Ross 308 achieves an indicative FCR ≈ 1.40. This is the lowest FCR in the whole cycle — a young bird converts feed into weight very efficiently. The earlier the collection, the lower the FCR (but also the lower the bird weight).
Day 42 — FCR approx. 1.50–1.53
A standard 42-day cycle gives an indicative FCR ≈ 1.50–1.53 according to Ross 308. This is the most commonly cited reference value for broiler production. A result above 1.60 at this age warrants investigation.
FCR rises with age
Each week the bird needs more feed per kilogram of gain — because part of the energy goes to body maintenance (vital functions) rather than growth alone. That is why flocks collected at 49+ days naturally have a higher FCR than 35-day flocks.
What drives FCR up — main causes
Respiratory and gut disease, poor feed quality (low digestibility), incorrect house temperature, feed wastage (poorly adjusted feeders, wet litter near drinkers), and an uneven flock (large spread in bird weights). More on nutrition and nutrient norms: broiler nutrition — norms.
Frequently asked questions about FCR in broilers
What is FCR in broilers?add
FCR (Feed Conversion Ratio) tells you how many kilograms of feed the flock consumed for every kilogram of live weight produced. Formula: FCR = total feed consumed (kg) ÷ total live weight (kg). The lower the result, the cheaper the rearing — the birds used less feed to produce each kilogram of weight.
What is a good FCR for broilers?add
It depends on the collection day and genetic line. Indicative values from Ross 308 Performance Objectives 2022: around day 35 FCR ≈ 1.40; around day 42 FCR ≈ 1.50–1.53. An FCR below 1.50 for a 42-day cycle is a very good result. An FCR above 1.65–1.70 requires a review of management and flock health.
What is the difference between FCR and EPEF?add
FCR measures just one thing: how efficiently feed is converted into weight. EPEF (European Poultry Efficiency Factor) is a composite indicator that also takes into account daily weight gain, mortality, and age at collection — the higher the better. FCR is part of the EPEF calculation. More about EPEF: EPEF in broilers.
Why does FCR rise as birds get older?add
An older, heavier bird needs more feed just to keep its body running (breathing, keeping warm, digesting) — this is called the maintenance requirement. As a result, each week a smaller share of the feed eaten goes into weight gain, and a larger share goes into maintenance. That is why FCR at day 49 is always higher than at day 35.
Do I include dead birds when calculating FCR?add
Yes — in the standard approach, only birds collected alive are counted in the live weight. Dead birds do not go into the weight, but the feed eaten by the entire flock (including birds that later died) goes into the numerator. This is why high mortality worsens FCR. Some systems calculate an "adjusted FCR" that corrects for mortality — it is worth knowing which method your integrator uses.
How can I improve FCR in the next cycle?add
Check in order: (1) feed quality and digestibility — poor raw materials are the most common cause of a high FCR; (2) flock health — gut disease destroys nutrient absorption; (3) house temperature — too cold or too hot raises FCR; (4) feed wastage — poorly adjusted feeders can waste several percent of feed; (5) litter moisture — wet litter correlates with health problems. You can track results from every cycle easily in the digital flock record.
Sources & resources
Calculate FCR automatically in DlaFerm.pl
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