How We Calculate

Our approach

A calculator is only useful if you can see how it reached its answer. Each HorseCalcs page explains its method in plain language, shows the formula where there is one and says which numbers are typical examples that you should replace. We use published guidance and standard formulas, and we do not take payment to favor a product.

Feed and hay

The feed calculator uses the National Research Council’s Nutrient Requirements of Horses (2007), which sets daily energy and protein needs by body weight and workload for an average mature horse. The hay calculator is based on the National Research Council’s recommendation that horses eat at least 1.5 percent of their body weight in forage a day, with most doing best around 2 percent when hay is the main feed, and it adds an allowance for waste, since hay fed on the ground or from round bales without a feeder is partly lost.

Weight and condition

The horse weight calculator uses the Carroll and Huntington formula, which estimates weight from heart girth and body length (heart girth squared times body length, divided by 330 for an adult). For average adult horses it lands within about 3 percent of true weight, which is better than guessing. The body condition calculator uses the Henneke 1 to 9 scale, developed by Dr. Don Henneke at Texas A&M in 1983, and averages the scores of six body areas.

Deworming and heat

The deworming guidance follows the American Association of Equine Practitioners, which now recommends strategic deworming guided by fecal egg counts, not a fixed rotation. The heat index tool uses the equine heat index that the AAEP and US Equestrian use, which adds the air temperature in degrees Fahrenheit and the relative humidity. It is not the same as the human heat index.

Tack and fit

Bit, blanket and saddle tools use standard measuring and sizing guidance used by tack shops and saddlery guides, and they say so. The rider weight calculator applies the widely used guideline that a horse should carry about 20 percent of its body weight or less, including tack, which goes back to US Cavalry manuals and is supported by a 2008 study at Wilmington College in Ohio. These tools give a starting point, and a proper fit needs the real horse and rider.

Barn, land and travel

The pasture, bedding, arena, fence, shipping and cost tools use typical coverage, density and price figures, and they show those figures so you can change them. The arena sand calculator, for example, turns length, width and depth into cubic yards and tons, using about 1.3 to 1.4 tons of dry sand per cubic yard and an allowance for compaction. The towing calculator adds weights, and the figure that counts is your vehicle manufacturer’s own rating.

Breeding

The foaling date calculator uses an average pregnancy of about 340 days, with a normal range of 320 to 370 days. The foal color calculator applies basic coat color genetics and shows probabilities, not certainties.

Converters

The converters use standard conversion factors. Hands are exactly 4 inches. One international foot is exactly 0.3048 meters, one acre is exactly 4,046.8564224 square meters, one U.S. gallon is exactly 3.785411784 liters and one avoirdupois pound is exactly 0.45359237 kilograms. Temperature converts with the usual Fahrenheit and Celsius formulas.

Finders

Each finder asks a few questions, scores your answers against the options and shows the best match, often with a runner-up. Some questions can force a result. For example, a horse that cannot chew hay is pointed toward cubed or chopped forage, and a mouth problem points toward bitless options. Each result explains why it fits, what to check and when it is not the right fit.

Limits

All results are estimates and general guidance. Real horses vary, defaults are examples and guidance changes. Please read our disclaimer and safety notes, and use the Report an Issue form if a result looks wrong.