Animal and Plant Calculators

These calculators answer the practical questions that come up with pets, gardens and backyard wildlife: how old a dog, cat or horse is in human years, how big a puppy will get, how old a tree is and how much sugar goes into a hummingbird feeder, and how many fish an aquarium can hold. Each one is built on published research data, shows its result in both US and metric units and explains how it got the number. They are free and run on phones and computers with nothing to install.

Calculators

What each calculator does

  • Horse Years Calculator: choose a breed or a type (light horse, warmblood, pony, miniature, draft, donkey or mule) and enter your horse’s age to get its age in human years, with its life stage from foal to geriatric. Breed data covers 51 breeds, a reverse mode converts human years to horse years, and the result shows the popular chart and the ×3 rule alongside for comparison.
  • Aquarium Calculator: pick your tank shape and enter its size to get the real water volume in gallons and liters, the filled weight, and the heater and filter it needs. Add fish from 191 freshwater, saltwater and brackish species to see how full the tank is and which fish do not mix.
  • Dog Years Calculator: choose a breed and enter your dog’s age to get its age in human years, based on lifespan data for 218 breeds. A reverse mode converts human years to dog years, and the result shows the AVMA chart, the DNA clock formula and the ×7 rule alongside for comparison.
  • Cat Years Calculator: choose a breed and enter your cat’s age to get its age in human years, with its life stage (kitten, young adult, mature adult or senior). A reverse mode converts human years to cat years, and the result shows the AAFP chart and the ×7 rule alongside for comparison.
  • Hummingbird Nectar Calculator: enter your feeder’s size and get the exact amount of white sugar and water for a 4:1 nectar, in cups, tablespoons, ounces or milliliters. It also tells you how often to change the nectar at your local temperature.
  • Tree Age Calculator: measure the trunk’s circumference at chest height, choose the species and your state, and get an age range from USDA Forest Service growth curves for 201 urban tree species. It also counts age from tree rings or from a known planting year.
  • Puppy Weight Calculator: enter your puppy’s age and current weight to estimate its adult weight and the age it will stop growing. Choose from 218 breeds or enter a mixed breed. The model was fitted to the growth records of more than 400,000 dogs.

Frequently asked questions

Are the calculators free?

Yes. Every calculator is free to use and needs no account.

How accurate are the results?

Each calculator gives a range rather than a single number where the data calls for one, and its article reports how often the real answer fell inside that range when the model was tested. A puppy’s adult weight and a tree’s age vary with genetics, diet and growing conditions, so the range is the honest answer.

Can I share a result?

Yes. Each calculator keeps your inputs in the page address, so copying the link shares the exact result.

Are there other interactive tools on the site?

Yes. The animal habitat maps show where animals live on a 3D globe, the animal 3D models can be turned and explored part by part, and the animal quizzes test how well you identify dogs, birds, snakes and fish from photos.

Card photos: Joshua J. Cotten and Marek Studzinski on Unsplash. Each calculator credits the photos it uses.