This guinea pig calorie calculator estimates your guinea pig’s daily energy needs from its weight and life stage, using the vet RER/DER formula. Just as important, it shows why guinea pigs are not calorie-counted like dogs or cats — and how to manage weight safely with diet and body condition instead.
A typical adult guinea pig needs very roughly 100–200 kcal a day, almost all of it from unlimited hay. Never ration hay to cut calories — it can cause deadly gut stasis.
Estimate daily energy needs (RER & DER) from weight and life stage.
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daily energy needs (DER)
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Resting (RER)
70 × kg⁷·⁷⁵
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Activity factor
Life stage
~80%
From hay
Not pellets
Current vs ideal weight — a safe plan that never rations hay.
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what to do
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Current
Weight
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Ideal
Target
Keep hay
Golden rule
Unlimited
Where a guinea pig’s calories actually come from.
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calories by food
Score your guinea pig’s shape by feel (the Size-O-Meter), 1 to 5.
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body condition
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Ideal score
Target
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Weigh
How often
Feel ribs
Method
Hands on
Estimated daily calories by guinea pig weight.
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calories by weight
How the Guinea Pig Calorie Calculator Works
The guinea pig calorie calculator estimates daily energy needs with the standard veterinary formula: Resting Energy Requirement (RER) = 70 × (weight in kg)0.75, multiplied by an activity/life-stage factor of about 1.2 to 2.0 to give the Daily Energy Requirement (DER). For a 1 kg adult that is roughly 105 kcal, and most adult guinea pigs are cited as needing somewhere around 100 to 200 kcal a day. But here is the crucial difference from dogs and cats: guinea pigs are hindgut fermenters that must graze constantly, so you never restrict their food to hit a calorie number. Treat this figure as background, and manage weight through diet balance (the 80/15/5 hay-veg-pellet ratio), body condition scoring, and weekly weighing.
Weight
RER
Adult DER (×1.5)
In pounds
600 g
~48 kcal
~72 kcal
~1.3 lb
800 g
~59 kcal
~89 kcal
~1.8 lb
1,000 g
~70 kcal
~105 kcal
~2.2 lb
1,200 g
~80 kcal
~120 kcal
~2.6 lb
1,400 g
~90 kcal
~135 kcal
~3.1 lb
Guinea pig energy data is limited, so these are estimates, not exact targets. The healthiest approach is unlimited hay plus a measured veg and pellet portion, checked against body condition — not calorie counting.
Daily Calories by Weight (Chart)
The chart shows estimated daily energy needs (adult maintenance DER) rising with body weight. Remember these are rough figures, and almost all of the calories come from hay that is always available.
How Many Calories Does a Guinea Pig Need Per Day?
A typical adult guinea pig needs roughly 100 to 200 kcal a day, depending on its weight, age and activity. Using the vet formula, a 1 kg adult works out to about 105 kcal (RER of 70 kcal × an activity factor of 1.5); a smaller 700 g pig needs less, and a larger or pregnant one more. These numbers are estimates because guinea pig energy requirements are not as well studied as those of dogs and cats. In practice you do not feed to a calorie target — you offer unlimited hay, a set veg and pellet portion, and let body condition and the scale tell you whether to adjust.
Can You Put a Guinea Pig on a Diet to Lose Weight?
Not in the calorie-restriction sense — and this is important. Guinea pigs are hindgut fermenters whose digestive system must keep moving constantly, so cutting their food, and above all rationing hay, can trigger gastrointestinal stasis or fatty liver disease, which can be fatal. To help an overweight guinea pig slim down safely: keep hay unlimited, reduce pellets to about 1/8 cup or slightly less, cut out fruit and sugary treats entirely, offer more low-calorie leafy greens, and encourage exercise and foraging. Aim for slow, gradual loss, and re-weigh weekly. Never crash-diet a guinea pig.
What Is an Unhealthy Weight for a Guinea Pig?
For an adult, a weight well outside the healthy range — below about 700 g or, for many pigs, above roughly 1,200 g for a female or 1,500 g for a male — is worth investigating, but the number alone does not tell the whole story. Body condition matters more: a guinea pig whose ribs and hips you cannot feel under a layer of fat, or whose belly nearly drags, is overweight (Size-O-Meter 4–5), while one with a sharp, bony spine and hips is underweight (1–2). Both extremes carry health risks — obesity raises the chance of bumblefoot, heart strain and diabetes, while sudden weight loss often signals dental disease or other illness. Check body condition and weigh weekly to stay on top of it.
What Is the 3-3-3 Rule for Guinea Pigs?
The 3-3-3 rule is a settling-in guideline, not a diet or calorie rule. It describes how long a newly adopted guinea pig takes to adjust: about 3 days to decompress and feel safe, 3 weeks to learn the routine and show its personality, and 3 months to feel fully at home. During those early days keep feeding simple and consistent — unlimited hay, fresh water, and the veg and pellets it already knows — and introduce new foods slowly. It has nothing to do with counting calories, but steady, stress-free feeding helps a new piggy settle in.
Frequently Asked Questions
How do I help an underweight guinea pig gain weight?
First see a vet, since weight loss is usually a symptom of illness such as dental disease, not just under-feeding. Then keep unlimited hay, add a little extra pellet, offer higher-calorie alfalfa and vitamin-C-rich veg, and for a struggling pig a vet may recommend a recovery formula like Critical Care given by syringe. Aim for a gradual gain of a few grams a day, not a sudden spike.
Can guinea pigs become obese, and why is it risky?
Yes. Too many pellets, fruit or sugary treats, plus too little space to move, lead to obesity. Overweight guinea pigs are prone to bumblefoot (painful foot sores), heart and joint strain, difficulty grooming, and a higher risk of diabetes. Manage it by keeping hay unlimited while trimming pellets and cutting treats, not by starving the pig.
Do pellets have more calories than hay?
Gram for gram, pellets are far more calorie-dense than grass hay, which is why the pellet portion is small (about 1/8 cup) and hay is unlimited. Hay provides a lot of a guinea pig’s daily energy simply because they eat so much of it, but it is bulky and self-limiting, so it does not cause weight gain the way over-feeding pellets or treats does.
How often should I weigh my guinea pig?
Weigh a healthy adult once a week on a digital kitchen scale, on the same day, and a sick or senior pig daily. Tracking the trend is the single best way to manage weight and catch illness early — a steady drop or climb over a few weigh-ins tells you far more than any calorie calculation.
Are carrots and fruit too high in calories for guinea pigs?
They are too high in sugar, which matters more than calories. Carrots, apple, banana and other fruits should be occasional treats only — a small piece once or twice a week — because regular sugary food promotes obesity and can contribute to diabetes. Stick to low-sugar leafy greens and bell pepper for daily veg.
Why aren’t guinea pigs calorie-counted like dogs and cats?
Because they are hindgut fermenters that must have food moving through their gut almost constantly. Restricting food or cutting hay to hit a calorie number can stall the gut (gastrointestinal stasis), which is a life-threatening emergency. Instead of calorie targets, guinea pig health is managed through the right diet balance, body condition scoring and weekly weight checks.
This guinea pig calorie calculator uses the standard RER = 70 × (kg)0.75 formula with life-stage activity factors of 1.2–2.0 for the Daily Energy Requirement, giving roughly 100–200 kcal a day for a typical adult. Because guinea pig energy data is limited and they are hindgut fermenters, these figures are background estimates, not feeding targets: weight is managed through the 80/15/5 hay-veg-pellet diet, body condition and weekly weighing, never calorie restriction. This is general guidance, not veterinary advice; a guinea pig losing weight or off its food needs a cavy-savvy vet promptly.
