How Much Should My Tortoise Weigh

How Much Should My Tortoise Weigh? the Calculation You Should Use

Knowing your tortoise’s correct weight can show you early signs that there may be problems with your tortoise diet or health. In the early years of your tortoise’s life, it is crucial to monitor their weight and keep it under check while they are growing. It allows you to judge if your tortoise needs more or less food more accurately. 

Once your tortoise becomes older, their weight becomes much less of an issue. However, it is still best practice to monitor it. Again it can give us early signs of a health problem that may need treating. Weighing your tortoise once they become an adult will become less frequent. 

A tortoise’s correct weight will be affected by age and size. There are two methods to see how much your tortoise should weigh. The Jackson Ratio and Donoghue Ratio both involve measuring the straight-line captive length to formulate the correct weight of your tortoise. 

The question of “how much should my tortoise weigh?” is notoriously difficult to answer. What is considered a healthy weight will have many caveats to it. Age and species will have the most significant bearing on what your tortoise should weigh.

Some species are much easier to check that they are within a healthy weight range. As we have some standard measurement methods, we can use them to make sure they are healthy.

Below we will help you discover the recommended methods to weigh your tortoise and weigh them correctly.   

Jackson Ratio

The Jackson Ration should only be used on the following two tortoises Testudo Graeca (Mediterranean Spur-Thighed Tortoise) and Testudo Hermanni (Hermanns tortoise).

The ratio is highly recommended by all experts in the tortoise field and is used to keep a close eye on your tortoise weight and size to ensure it is within a perfect range. If you want to hibernate your tortoise, you will want to make sure your tortoise is healthy. Part of this is their weight to get through the hibernation process successfully. 

The Jackson ratio calculation sounds complicated, but it is very simple you take the weight in grams of your tortoise and divide it by the cube of the carapace length in centimeters. It will give us a density of our tortoise in g/cm3.

A reading between 0.19-0.21 is the ideal weight and shows you have everything just right, and it would be safe to hibernate your tortoise. Anything below 0.19 would be considered underweight and not safe to hibernate. Over 0.21, and your tortoise could be overeating. If you have a female tortoise, anything over 0.23 could indicate they are carrying eggs or are incredibly overweight. 

The great people at tortoise-protection-group have made us a straightforward calculator, so we don’t have to do the math. 

Donoghue Ratio

A more generic calculation to use is the Donoghue ratio, and it can be applied to all other tortoise species. In contrast, the Jackson ratio can only be used on two species. 

It is a basic formula that gives us an ideal weight for our tortoises. 

SCLcm3 x 0.191 = tWTgr

You take the straight line captive length cubed times 0.191 equals the ideal weight in grams.

You must measure in centimeters to give a more accurate reading. 

If you want to work in inches, then the formula is calculated as followed:

SCLcm3 x 0.113 = tWToz

This gives us the weight in ounces and is less accurate than using centimeters as your measurement. 

Tortoise BMI

With the above workings, we can now work out our tortoise’s BMI to see how over or underweight their current state. With this knowledge, we can then decide if there is any action we need to take.

cWT/tWT = tBMI (the formula represents tortoise current weight divided by the Donoghue Ratio equaling their BMI)

Tortoise BMI Calculation Example

SCL (Straight-line Carapace Length) of 14.3 centimeters and a current weight of 380 grams

Donoghue Ratio – 14.3^3 x 0.191 = 558.5
BMI Calculation – 380/558.5 = 0.68
BMI Result – 0.68 Dehydrated and/or underfed. Offer appropriate care

This quick tip allows Google to calculate the Straight-line Carapace Length/Cubed times 0.191; you will need to change the first number to the correct measurement in centimeters of your tortoise.

Tortoise BMI Ranges

BMI RangeAdvice
0.66 or lowerVery dehydrated. Seek or offer immediate care
0.66 to 0.83Dehydrated and/or underfed. Offer appropriate care
0.83 to 0.99A little underweight. Review and correct care and diet as appropriate
1.00‘Ideal’ target weight. You will rarely get this, even with the best care
1.01 to 1.16A little overweight. Review and correct care and diet as appropriate
1.16 to 1.33Overweight. Adjust your tortoise care and diet
1.33 or overObese. Seek or offer proper care

The above figures should be used as guidelines only.

How to measure your tortoise correctly

Both the above measurements use the Straight-line Carapace Length, which is where people go wrong in the calculation. People go wrong by measuring over the top of the shell. Going end to end without going over the top can be a little tricky.

The easiest way without buying fancy tools is by placing a piece of paper on the floor against a wall. 

We then take our tortoise and place them right up to the wall, so their head retracts. If you are careful, it is completely fine and will cause your tortoise no harm.  

You then mark the paper with a pen at the back of the carapace. We can now let our tortoise get on with their day. Now we have a very accurate reading of our tortoises Straight-line Carapace Length, which allows us to take the measurement from the paper with a ruler without any fancy tools required. 

How Important is Weight Monitoring?

Many within the tortoise community do not monitor their tortoise weight or size. However, this is fine if you have everything like diet and health issues all dialed down. 

These people will weigh their tortoise before hibernation to ensure they are at the correct weight but rarely before this event. 

Now, I’m not in this camp and feel something that can be done so easily and quickly shouldn’t be skipped. As it can give us early signs of health a feeding issues that don’t outwardly display themselves. 

There are two camps where you fall will be a personal thing, and I found once a month weight monitoring was so easy I carried the practice on. I can say that my vet loves to see my tortoise weight monitor sheet and says it makes her job so much easier. 

What Causes Weight Loss?

If you have stumbled upon this page, there will be few reasons. You are just unsure what your tortoise should way or feel your tortoise is over or underweight. Below I look to give some of the common reasons that your tortoise can be over or underweight.  


Just as the human body, tortoise bodies are made up of water, and many weight problems come from dehydration. 

Baby tortoises suffer from dehydration much more than their adult counterparts. Adult tortoises are much better at taking on the water, where baby tortoise needs to learn the skill over time. A skill they need and one we need to encourage by placing them into shallow bowls of water.

Spraying food with water will also allow your tortoise to take on more needed water or offering food high in water. A baby tortoise needs lots of water as its body is actively growing.

Poor Diet

Just as a lack of hydration can cause weight loss, a poor diet can have both side effects of weight loss and weight gain. 

A diet should as closely as possible follow the one they would follow in the wild. Rich, healthy greens will make up the bulk of their diet with very little fruit. 

One mistake you often see is feeding just iceberg lettuce due to how easy it is to purchase. However, iceberg lettuce is made up of mostly water and minimal vitamins and minerals your tortoise needs. Iceberg lettuce is an excellent way to offer more water, but when eaten exclusively can lead to dramatic weight loss.   


Despite not being the most common weight loss problem, gastrointestinal parasites can cause both wild and captive tortoise problems. People ask do tortoises attract bugs they don’t their enclosures do, and the reason to keep them clean is to keep parasites away. 

A parasite infection can cause your tortoise all sorts of problems, from a loss of appetite to vomiting. If you feel your tortoise has an infection, you should seek veterinarian advice. 


So there is no universal answer to how much should my tortoise weigh, but there are calculations to help you discover the correct weight.

Both the Jackson Ratio and Donoghue Ratio are highly recommended by expert tortoise keepers worldwide and the method I use to indicate any weight issues with my tortoise. Keeping a record of your tortoise weight will help you or your vet quickly spot any problems. Weight monitoring can help you pinpoint a problem before they become apparent

Some tortoise owners will say get the diet right, and you don’t need to weigh your tortoise. I don’t go along with this; it takes a few minutes once a month to make sure my tortoise is staying healthy. When my tortoise was a baby, I weighed them once a week; it wasn’t a chore, which helped me keep them healthy.