Weight
Your guinea pig's weight is one of the most important indicators of its health and wellbeing. As such it is very important that you track and monitor your pets' weight over time, to see if they are developing normally, and so that you can spot any unusual changes early and act quickly. The following guide describes what is considered to be a 'normal' guinea pig weight at various ages, and also describes how to measure it.
Birth
When they are born, you can expect your guinea pigs to weigh anything from 60 to 120 grams. Although this is a wide variation, it is perfectly natural, and is dependent upon a number of factors - different breeds tend to weight different amounts, and a larger litter will generally produce lighter pups. Probably the best indicator is the babies' relative weights. For example, if your guinea pig has given birth to 4 pups, with 3 weighing around 100 grams and the other weighing just 60 grams, it is probably wise to monitor this pup more closely.
Newborn pups are very small, typically weighing between 60 and 120 grams. Image by wstryder.
Growth
As your guinea pigs grow and mature, you should be able to see theirsize and weight increasing gradually and consistently. This will take place quite rapidly to begin with, at a rate of around 30-50 grams per week. As they reach adulthood, this weight gain will begin to decline, and eventually stop at somewhere around 12 to 14 months old. During this time you may notice that males gain more weight than females. This is perfectly natural, and is not cause for concern. As a rough guide, a female (sow) will typically weigh about 20-25% less than a male (boar).
Maturity
Once they reach full maturity, your cavies should plateau at weights of around 900-1,200 grams for a male and 700-900 grams for a female. Again, this depends on factors such as breed, and it isn't cause for concern if your pets are slightly above or below this. However, as always, if you are in any doubt, you should consult a vet as soon as possible.
A fully grown guinea pig can weigh over a kilogram.
Weighing
You don't need any specialist equipment to weigh your guinea pig - an accurate set of kitchen scales is more than good enough for the job. To weigh your pet, simply place it in on the scales, wait for it to settle down and stay still, and then record the reading. If your pet fidgets and moves around a lot, it can often be a good idea to place them in a bowl or tin during the weighing - just remember to subtract the weight of the bowl or you'll get inaccurate readings.
You can weigh your guinea pig using a standard set of kitchen scales. Image by Plastic_Bat.
Tracking
Monitoring your guinea pigs' weight is absolutely essential. Guinea pigs have a very strong survival instinct, and part of this involves disguising any weaknesses (including illnesses) for as long as possible. Because of this, it is quite common for a cavy to look perfectly health when in fact it needs medical attention. Any sudden changes or prolonged decline in the weight of your pet are an excellent indicator that something is wrong, and so it is wise to get into the habit of measuring and recording your animals' weight on a weekly basis.
Keep a record of your cavies' weights in a book or on your computer. A spreadsheet is ideal because it also allows you to plot a graph, which is an even easier way to spot weight changes and trends. If you notice anything unusual, you should act quickly and take your pet to the vet to get it properly examined. Be sure to take your weight record with you as well, as this could provide the vet with useful information to help make a diagnosis.
If your pet does fall ill, you should increase your monitoring frequency from weekly to daily. This will allow you to keep an eye on any short-term changes and help you to monitor your guinea pig's recovery.
Pregnancy
One thing to be aware of is that a pregnant sow can get significantly heavier during the gestation period (59-72 days), and it is not uncommon for her weight to go up to as much as double its usual level. This is perfectly normal, but again it is wise to monitor it for any sudden changes, as these may indicate a problem with the pregnancy, and require urgent medical attention.