How to weigh a horse without a weighbridge: tape, formula and how accurate they are

Multiply heart girth by heart girth by body length, in centimetres, and divide by 11,900 to get kilograms: a 185 cm girth and 170 cm length gives 489 kg. A weigh tape is quicker but reads about 6% light.

Neither is a weighbridge. Both are good enough for the job that matters most at home, which is noticing that the number is moving.

This post covers how to use a weigh tape properly, the metric formula with a worked example and a ready reckoner, how accurate each method really is, and what to do with the result.

Quick reference

• Formula: girth (cm) x girth (cm) x length (cm) ÷ 11,900 = kg
• Girth: just behind the elbow, up over the withers, read on the out-breath
• Length: point of the shoulder to point of the buttock
• How often: every two weeks, same tape, similar time of day
• Accuracy: a weigh tape averaged 5.7% light against a weighbridge, more in heavy types
• Best use: spotting a trend, not dosing to the last kilo

How do you weigh a horse with a tape?

A weigh tape is a tape measure printed with kilograms instead of centimetres, so you read the weight straight off the girth. The method in the 2023 weighbridge study in Animals and in British Equestrian’s weigh taping guide is the same:

1. Stand the horse square on firm, level ground, weight even over all four feet, head relaxed in its normal position.
2. Place the tape just behind the elbow and take it up over the withers, so it runs at a slight angle around the barrel where a girth would sit.
3. Snug, not tight. The tape should lie flat on the coat without digging in.
4. Read it as the horse breathes out.
5. Use the right side. World Horse Welfare notes that the most accurate tapes have a horse side and a pony side, so pick the one that matches your horse’s height.
6. Write it down with the date and time of day.

A helper to hold the horse makes this far easier, and a horse that is fidgeting or standing with a hind leg rested will not give you a fair reading.

What is the formula for a horse’s weight in kg?

Weight (kg) = heart girth (cm) x heart girth (cm) x body length (cm) ÷ 11,900.

The formula comes from Carroll and Huntington’s 1988 study in the Equine Veterinary Journal, which weighed and measured 372 horses of mixed breeds, heights and fatness in Australia. For the 281 horses whose girth and length were also measured, girth squared times length explained 90% of the variation in real weight (r² = 0.90). The average constant in their data was 11,900, and that is the one I use here because it is the figure the authors published.

You will see other numbers. A 2020 study of 299 horses in Poland wrote the same formula with 11,877. It makes almost no difference, as the worked example shows. What matters is using the same constant every time.

Worked example. A horse with a 185 cm girth and a 170 cm length:

• 185 x 185 = 34,225
• 34,225 x 170 = 5,818,250
• 5,818,250 ÷ 11,900 = 489 kg

With 11,877 you get 490 kg. With a girth 1 cm bigger, 186 cm, you get 494 kg. So a centimetre of slack in the tape moves the answer more than the choice of constant does, which is why consistent technique matters more than the maths.

If your tape is in inches, multiply each measurement by 2.54 to get centimetres first.

Ready reckoner

Weights in kg from the formula, rounded. Find your horse’s girth on the left and the length closest to yours across the top.

How do you measure a horse for the weight formula?

You need an ordinary soft tape measure, a pen and ideally a second person.

1. Stand the horse square on level ground, as for a weigh tape.
2. Girth: pass the tape behind the elbow and over the withers, and read it in centimetres on the out-breath.
3. Length: measure from the point of the shoulder, the bony point at the front of the chest, straight along the side to the point of the buttock, the bony point at the back of the hindquarters. A helper holding the zero end makes this a two-second job.
4. Measure twice. If the two readings differ by more than a centimetre or two, do it a third time.
5. Same time of day. British Equestrian suggests taking readings at a similar time, because weight shifts a little through the day with eating and drinking.
6. Do the sum or use the table above.

Mark the points of shoulder and buttock with chalk the first time if you struggle to find them. Measuring to the same landmarks every fortnight is what makes the trend honest.

How accurate is a weigh tape compared with a weighbridge?

Less accurate than most of us assume for a single reading. The 2023 Animals study compared one widely sold PVC weigh tape against weighbridge weights for 1,716 horses over two years old, collected through a feed company’s nutrition consultations:

• The tape read 32.8 kg light on average: 451.6 kg against a true 484.4 kg.
• That is a mean error of minus 5.7%.
• Individual horses ranged from 151 kg under to 64 kg over.

The authors concluded that tapes generally underestimate, particularly in heavier horses, and that breed, bone and fat cover all affect the reading.

The formula does better because it adds body length, but it is not exact either. In the 2020 Polish study, the Carroll and Huntington formula came out lower than the scale on average in every group:

It was the closest formula of those tested for Thoroughbreds, and further out for the heavier Polish warmblood breeds, reading 29 to 39 kg low on average. The best formula differed from one breed group to the next.

So the honest ranking is weighbridge, then formula, then tape, with none of the home methods precise to the nearest few kilos.

Which horses does a weigh tape suit badly?

The ones built differently from an average riding horse. In the 2023 weighbridge study:

So the cob, the draught cross and the chunky warmblood are the horses most likely to be told they weigh less than they do. On a horse that really weighs 600 kg, 8.5% is about 51 kg. Fatter horses also read heavier for the same true weight, by about 1.2 kg for each half point of body condition score.

Both studies here measured adult horses only. Neither says anything about foals, youngstock, minis or pregnant mares, so I would not lean on a tape or formula for any of those. Ask your vet.

Why does knowing your horse’s weight matter?

Three reasons, in order of how often they come up on a yard.

Wormer and medicine doses. Wormers are dosed by bodyweight. The Animals paper notes that under-dosing may let resistant parasites survive, and a tape that reads 50 kg light on a cob is exactly how that happens. Use the best weight you can get, and ask your vet or SQP if your horse sits near the edge of a dose band.

Feeding. Forage and feed are worked out as a share of bodyweight, so a weight that is wrong by 10% makes the ration wrong by 10% too. Our guide to how much hay a horse needs uses the weight you get here.

Spotting slow change. Winter is when a horse quietly drops condition under a rug, or a good doer quietly gains it. World Horse Welfare links being overweight to laminitis and extra strain on the heart, lungs and joints, and our post on the early signs of laminitis covers what to watch for. Coming back into work after a break is another time a baseline helps, which getting a horse fit after time off goes into.

How often should you weigh tape a horse?

Every two weeks, with a fat score at the same time. The BHS fat scoring guide says weigh tapes may not be 100% accurate but are a good tool to monitor whether your horse is holding, losing or gaining weight, and suggests using one alongside fat scoring every two weeks. British Equestrian and World Horse Welfare both say roughly fortnightly too.

This is where the accuracy problem mostly disappears. If your tape reads 6% light, it reads 6% light every time, so a fall from 480 to 465 over a month is still a real fall of about 15 kg on that tape. Keep these the same each time:

• the same tape, and the same side of it
• the same spot behind the elbow
• a similar time of day, before or after feeding as usual
• ideally, the same person

Then look at the line over two or three months, not at any single number.

Where can you find a horse weighbridge?

The BHS says it can bring a weighbridge to a yard, and that vet practices or feed companies may offer the same. In practice, ask your vet first, then your feed merchant or the helpline of the feed brand you use.

When you do get on one, measure your horse with your own tape and your formula the same day. Now you know how far your tape reads from the truth for this horse, and every fortnightly reading after that is worth more.

When should you call the vet about your horse’s weight?

A tape tells you a number moved. It cannot tell you why. Ring your vet if your horse:

• Loses weight steadily for no reason you can see, or drops weight quickly over a couple of weeks
• Loses weight while eating well, or is struggling to eat or dropping food
• Goes off its food or water
• Gains weight fast, especially with a cresty neck or fat pads appearing
• Shows weight change alongside heat in the feet, a strong digital pulse, reluctance to walk, dullness or any sign of colic: ring straight away for these

And if a dose really matters, such as a wormer for a horse near a band boundary or any medicine your vet prescribes, ask for a weight rather than relying on a tape.

Where the technology fits

Plainly: Stride does not record your horse’s weight. There is no weight field, no weigh tape log and no formula calculator in the app, and nothing in it works out a wormer dose.

What it does track sits alongside the weighing you do by hand:

• The Body & Condition scan takes a side-on photo and gives an estimated body condition score out of nine, kept as a trend alongside earlier scans. It is an estimate from a picture, so use it as a prompt to fat score by hand, not as a replacement.
• Feed records what you give and, where you enter amounts in kilograms or grams, shows the total fed per day, which is the other half of any weight question.
• Notes keep anything else, so you can write your fortnightly tape reading there with its date if you want it on the same timeline.

It is a record, not an adviser. The tape, the fat score and, when it matters, your vet make the call.

If you take one thing from this: measure your horse this weekend, write the number down, and do it again in two weeks. The second reading is the useful one.