Reptile Prey Size Calculator

Reptile Husbandry Tool

Reptile Prey Size Calculator

Estimate a safe, appropriately-sized feeder for your snake based on its body weight and life stage — and see exactly which standard feeder rodent fits.

Reptile body weight (current weight of the animal)

Please enter a valid body weight.

Species group

Life stage / goal

Recommended Feeding

Best Feeder Match

Target Prey Weight

Feeding Frequency

Overview

The Reptile Prey Size Calculator takes the guesswork out of one of the most common — and most consequential — decisions in snake keeping: how big the next meal should be. Feeding prey that is too large is a leading cause of regurgitation and stress, while feeding prey that is too small slows growth and leaves the animal undernourished.

This tool is built for hobbyist keepers, breeders, rescues, and pet-shop staff who want a fast, defensible starting point grounded in widely accepted husbandry practice. You enter your animal's current weight, species group, and life stage; the calculator returns a target prey-weight range, the matching standard feeder rodent (pinky through jumbo rat, up to rabbits for giant constrictors), and a sensible feeding interval.

How It Works

Weigh your reptile and enter its current body weight, choosing the unit (grams, kilograms, ounces, or pounds).
Select the species group so the tool can favour the feeder type (mice, rats, or rabbits) typical for that animal.
Pick the life stage — growing animals need proportionally larger, more frequent meals than adults on maintenance.
Press Calculate. You'll get a target prey-weight range, the closest standard feeder size, and a recommended feeding interval, with a full breakdown.

Formula Explanation

The calculation rests on the long-standing keeper rule that a meal should be a modest percentage of the animal's body weight, scaled by life stage:

Prey weight = Body weight × Target %

Hatchling / Growing: 13%–18% of body weight — supports active growth.
Juvenile: 10%–15% of body weight — steady development.
Adult (Maintenance): 8%–12% of body weight — maintains healthy condition.

A second, visual check is applied: the girth rule. The prey item should be no wider than roughly 1 to 1.5× the widest part of your snake's body. The resulting weight range is then matched to real feeder-rodent sizes so you can buy the correct item.

Practical Benefits

Prevents regurgitation: avoids oversized meals that snakes commonly bring back up.
Supports healthy growth: keeps juveniles on an appropriate upward curve without power-feeding.
Saves money: buy the right feeder size the first time instead of trial and error.
Reduces obesity risk: right-sized adult meals prevent the fatty-liver and joint problems linked to overfeeding.
Great for record-keeping: gives breeders and rescues a consistent, repeatable feeding baseline across many animals.

Frequently Asked Questions

As a rule of thumb, a meal should weigh about 8%–18% of your snake's body weight depending on life stage, and the prey item should be no wider than roughly 1–1.5 times the thickest part of the snake. If a meal leaves a noticeable, lasting bulge that doesn't go down within a day or two, it was likely too large.

When in doubt, choose the smaller feeder. It is far safer to slightly underfeed than to overfeed. You can always feed a little more frequently, or move up a size at the next feeding once you confirm the animal handles the meal comfortably with no regurgitation.

Growing snakes generally eat every 5–10 days, juveniles every 7–14 days, and adults every 10–21 days, with slow-metabolism species like ball pythons and large constrictors on the longer end. The calculator suggests an interval, but always adjust to your animal's body condition, appetite, and the advice of an experienced reptile veterinarian.

This calculator is designed specifically for whole-prey-eating snakes. Monitors, tegus, and many lizards eat varied diets (insects, eggs, multiple prey items) with very different ratios, and herbivorous or omnivorous reptiles differ entirely. For those animals, use the result only as loose context and consult a species-specific care guide or a qualified vet.

Disclaimer: This calculator provides general educational estimates based on common husbandry guidelines and is not veterinary advice. Individual reptiles vary by species, morph, age, health status, and reproductive condition. Always assess your animal's body condition, monitor for regurgitation or weight problems, and consult a qualified reptile veterinarian before making feeding decisions. The creators of this tool accept no liability for outcomes resulting from its use.