Cat Calorie Needs (MER + Body Condition)
Calculate daily cat calories and food portions
Cat calorie needs, MER and body condition FAQ
How many calories should my cat eat per day?
There is no single magic number for every cat, which is why a cat calorie calculator is so useful. This tool estimates your cat’s maintenance energy requirement (MER) based on body weight, life stage, activity pattern and body condition score (BCS). A lean, indoor, neutered cat usually needs fewer calories than an active outdoor hunter or a growing kitten.
What are RER and MER in feline nutrition?
RER (resting energy requirement) is the baseline number of calories a cat would need at rest in a neutral environment. It’s often calculated as 70 × weight(kg)0.75. MER (maintenance energy requirement) adds multipliers for growth, neuter status, activity and body condition so it better reflects real-life cat calorie needs.
How does body condition score (BCS) change calorie recommendations?
The BCS is a 1–9 scale describing how lean or heavy a cat is. Ideal cats are usually scored 4–5/9, with a visible waist and ribs that can be felt but not easily seen. Underweight cats may need more calories, while overweight and obese cats usually need fewer calories and a structured weight-loss plan. This calculator nudges calories up or down around the ideal MER when you mark your cat as underweight or overweight.
Can this calculator help with weight loss for overweight cats?
The tool can highlight that an overweight cat’s current calorie intake is probably too high, but safe weight loss needs a plan from your vet. For true weight-loss diets, vets often use lower factors and more frequent monitoring than a simple maintenance cat calorie calculator provides. Use the result as a conversation starter, not a full weight-loss program.
How do I read the calories on my cat food label?
Most labels list energy as kcal per 100 g and sometimes also kcal per can or pouch. Enter whichever value you have and the calculator will convert your cat’s MER into grams per day and/or cans per day. Always confirm whether the numbers refer to “as fed” or “dry matter” and stick to one product at a time when you’re fine-tuning portions.
Does indoor vs outdoor really affect cat calorie needs?
Yes. Indoor-only cats often spend more time resting or gently exploring and usually burn fewer calories than outdoor cats that roam, climb and hunt. The activity dropdown lets you choose indoor, mixed or outdoor so the MER reflects those different energy levels without making the calculator complicated.
Should I change calories as my cat moves into a senior life stage?
Many senior and geriatric cats become less active but may have changing metabolism or medical conditions that affect calorie needs. This calculator gently adjusts MER for senior life stage, but the real key is to monitor weight trends, muscle condition and BCS. If weight or appetite change suddenly, contact your vet rather than just tweaking food grams.
How to use this cat calorie needs calculator
The goal is to keep cat calorie maths simple enough to use every day. You only enter weight, life stage, activity and body condition, plus a couple of optional food label values, and the calculator handles the RER → MER conversion and portion size.
1. Enter an accurate body weight in pounds or kilograms
Start with the current body weight. By default the tool uses pounds (lb), but you can switch the units box to kilograms (kg) if that’s what your scale shows. Behind the scenes, the number is converted to kg for the RER equation and then shown back as both lb and kg on the summary card.
2. Choose life stage, activity and BCS
Next, pick the most accurate life-stage and neuter status option, your cat’s lifestyle / activity level and their body condition score band. Together, these sliders tell the calculator whether your cat is a growing kitten, a typical indoor adult, an outdoor hunter, or a senior that needs a gentler maintenance range.
3. Add your cat food label (optional but powerful)
To turn calories into real-world grams or cans per day, add the numbers from your cat food label:
- Enter kcal per 100 g to get feeding amounts in grams.
- Enter kcal per can / pouch to see how many packs per day to feed.
- You can fill in one or both, depending on how the label is written.
4. Read the daily calories and portion suggestions
Tap Calculate calories and the result card shows a headline like “MER ≈ 220 kcal/day (adult, neutered, indoor)” plus a breakdown of weight, life stage, activity and BCS. If you entered label data, the right-hand column converts this MER into grams per day and/or cans per day, plus approximate per-meal portions assuming two meals.
5. Copy the summary for notes or vet visits
Use the Copy summary button to grab a text-friendly version of the calculation. You can paste it into a notes app, share it with family, or bring it to your next vet appointment as a starting point for a feeding plan. Over time, you can adjust calories up or down while tracking your cat’s weight and BCS to keep them in a healthy, lean condition.
Always treat these numbers as a structured estimate, not a rigid rule. If your cat’s weight, appetite, thirst or behaviour don’t match what the calculator suggests, that’s a sign to check in with your vet about individual nutrition and calorie targets.
How the cat calorie math works (RER, MER, activity and BCS)
Behind the scenes, the calculator turns your inputs into a daily calorie target using a two-step feline energy equation.
Step 1 · Resting energy requirement (RER)
First, we convert weight into a resting energy requirement:
RER = 70 × weight(kg)0.75
This gives a baseline “lying on the sofa all day” calorie need that works across a wide range of cat sizes. Whether you start from pounds or kilograms, the value is converted into kilograms before this step.
Step 2 · Maintenance energy requirement (MER)
We then multiply RER by factors for life stage, activity and body condition to estimate MER:
- Life stage & neuter: kittens and entire adults get higher multipliers; senior and neutered cats slightly lower.
- Activity level: indoor / calm cats are nudged down; outdoor hunters are nudged up.
- BCS band: underweight cats are nudged above ideal; overweight cats are nudged below it.
The combined factor typically lands somewhere between about 1.0 and 2.5 × RER for most healthy pet cats. The final MER is rounded to a practical number so it’s easy to remember and use.
Converting calories into grams and cans
When you enter kcal per 100 g, the calculator divides MER by that value and multiplies by 100 to estimate grams of food per day. When you enter kcal per can / pouch, it divides MER by that number to estimate cans or pouches per day. Portions are then halved to give an approximate per-meal amount for twice-daily feeding.
This isn’t a perfect biological model, but it matches how many vets and nutrition guides explain cat calorie calculations: start from RER, scale for real life, then turn the result into clear, repeatable feeding amounts you can adjust based on weight and BCS over time.
References and further reading on feline calories and body condition
Use these resources alongside this calculator to fine-tune your cat’s nutrition plan:
- WSAVA Global Nutrition Guidelines — overview of nutritional assessment, RER / MER concepts and practical feeding advice for dogs and cats.
- WSAVA Cat Body Condition Score Chart (1–9) — visual guide to underweight, ideal and overweight feline body condition scores.
- AAHA/AAFP Feline Life Stage Guidelines — Nutrition and Weight — discussion of how life stage, neuter status and activity affect feline energy needs.
- Pet Nutrition Alliance — Calorie Calculator — veterinary calorie calculators and educational material on dog and cat energy requirements.
Whenever your cat’s health, appetite or weight changes, treat this cat calorie calculator as a starting point for questions and ask your vet how to adapt MER, BCS targets and feeding amounts to your individual cat.