How to Calculate your Horse’s Weight

On a recent visit from my local veterinary practise the conversation of horse weight came up, where my duty vet told me that the practise now had accurate horse scales. We discussed just how hard it is to visually assess horse weight and that without the scales the assumed weights were generally far off the mark. 
 

Now, like the average horse owner, my funds do not stretch to purchasing horse scales, yet I do need to know my horse's weights with a good degree of accuracy for three reasons:

• The correct administration of horse wormers and other drugs
• Monitoring the horse’s condition for weight changes
• Assessing your horse’s strength.

To complicate the picture, inaccurate horse weight calculating methods abound. Sure, weight tapes are an alternative and these do not involve calculations. So they are easy to use but they also significantly underestimate the real horse weight. An example of this is given below.

This level of inaccuracy just means you must know how to accurately calculate your horse’s weight. However, horses come in all types so it is very difficult to find a formula that works for all horses. Next, we will look at this problem in greater depth by considering the generally accepted weight formula.

What is the Formula to Calculate Horse Weight?

The most commonly used formula is well-documented and involves two calculations that are easily made on a calculator. You must know your horse's girth measurement and body weight for this formula. Then just do as I have outlined below.

• Multiply together girth circumference x girth circumference x body length.
• Divide this value by 330 to give the horse’s weight in pounds.

Alternatively, there are online horse calculators that will show how to measure your horse's girth and length. You can then enter the data and a weight will be calculated for you.  However, although this formula is widely used it gives inaccurate results for big-framed horses.

So How do I Accurately Calculate my Horse’s Weight

Many equestrians use the generally accepted formula but add on 50 pounds to arrive at a more accurate figure. However, research shows that this still underestimates the weight of larger framed quarter horses and tall warm-blood horses. Now, over the years I have been able to stand a number of horses on two different farmer's weighbridges, This permitted me to compare the formula calculation with actual horse weight for a number of horse types. From these results, my conclusions are as I outline here.

• Use the generally accepted formula with short thoroughbred/ and lightweight warm-blood horses.
   
• Add 50 pounds to the formula calculation for short middle-weight horses.
   
• Add 100 pounds for short heavy-weight horses (eg cobs and quarter horses).
   
• Add 50  pounds to the calculation for tall thoroughbreds and lightweight warm-blood horses.
   
• Add 100 pounds to the calculation for tall middleweight horses.
   
• Add 150 pounds to the calculation for tall heavyweight horses

Please note, that I have never weighed ponies and do not have information on the accuracy of the general weight formula with these smaller equines.

The take-home Message

Your horse's weight can be accurately known using livestock scales or a weighbridge. However, a calculation will give a very good approximation if the horse type is considered and adjustments are made. Weight tapes are very inaccurate but will tell you if your horse's girth is expanding. So will any tape measure if you can find one long enough to go around your horse's girth?