# Snake prey size calculator

> Pick your species and enter one measurement to get a prey size range: widest body width for corn snakes, body weight for ball pythons. Both rules come from the ReptiFiles care guides.

## What size prey should a snake eat?

Corn snakes take prey 1–1.5× their widest body width, not head width: a snake 5.0 cm wide at its widest point takes prey 5.0–7.5 cm wide. Ball pythons take 10–15% of body weight, so a 400 g snake gets a 40–60 g meal. Both rules come from ReptiFiles.

Use the interactive calculator on the page: https://petguidecalc.com/reptile/prey-size-calculator/ — pick a species and enter the widest body width (corn snake) or body weight (ball python) to get the prey size range.

## Prey size rules at a glance

| Species | Method | Formula | Source |
|---|---|---|---|
| Corn snake | Prey width | Prey width = 1–1.5× the snake’s widest body width, not head width. | ReptiFiles — Corn Snake Care |
| Ball python | Prey weight | Prey weight = 10–15% of the snake’s body weight. | ReptiFiles — Ball Python Care |

## How prey size is determined

Corn snakes are sized by body width. Measure the snake at its widest point, then choose prey 1–1.5× that width. ReptiFiles (Corn Snake Care Guide) is explicit that the head is the wrong reference: it is narrower than the body, so head-based sizing gives meals that are too small.

Ball pythons are sized by weight. Weigh the snake in grams, then take 10–15% of that number as the prey weight: a 400 g ball python takes a 40–60 g meal. Weigh the prey too; eyeballing size drifts, especially once prey thaws and softens.

A meal can be several smaller prey. Add the weights together and keep the total inside the 10–15% band: two 22 g mice sum to 44 g, which fits inside the 40–60 g band for a 400 g ball python. The calculator returns a range, not a single target; start at the lower end for a young or thin snake.

## Prey size FAQ

**Q: What size prey should a corn snake eat?**

Prey about 1–1.5× the snake’s widest body width, never the head. Measure the widest point of the body: a snake 5.0 cm wide there takes prey 5.0–7.5 cm wide. The rule comes from the ReptiFiles corn snake care guide.

**Q: How much should a ball python eat per meal?**

A meal weighing 10–15% of the snake’s body weight, per the ReptiFiles ball python care guide. A 400 g ball python takes a 40–60 g meal, and a 1000 g adult takes 100–150 g. Weigh the prey rather than guessing.

**Q: Can I feed a ball python two smaller prey instead of one larger one?**

Yes, if the combined weight lands inside the 10–15% band. Two 22 g mice sum to 44 g, inside the 40–60 g band for a 400 g ball python. Add up every item before feeding, and trim the next meal if the total runs high.

**Q: Why should corn snake prey be sized by body width, not head width?**

Because the head is narrower than the body at its widest point, so head-based sizing under-feeds. ReptiFiles recommends 1–1.5× the widest body width, which keeps meals large enough without overloading digestion.

**Q: How do I measure body width or weigh my snake?**

Measure the widest point of the body with a flexible tape while the snake is at rest; never the head. Weigh the snake on a digital kitchen scale in grams, and weigh each prey item the same way. The ReptiFiles care guides describe both steps.

## More reptile tools

- [Reptile care tools](/reptile/)
- [Snake feeding frequency calculator](/reptile/feeding-calculator/)
- [Pet snake care guide](/reptile/snake-care/)

## Sources

The two sizing rules come from the ReptiFiles care guides for corn snakes and ball pythons.

- [Scaling Relationships of Maximal Gape in Two Species of Large Invasive Snakes, Brown Treesnakes and Burmese Pythons, and Implications for Maximal Prey Size](https://doi.org/10.1093/iob/obac033) — Jayne BC, Bamberger AL, Mader DR, Bartoszek IA, Integr Org Biol, 2022.
- [Corn Snake Care Guide](https://reptifiles.com/corn-snake-care/) — ReptiFiles, reptifiles.com, no date. Source for the prey width rule: size prey to 1–1.5× the snake’s widest body width, not the head.
- [Ball Python Care Guide](https://reptifiles.com/ball-python-care-guide/) — ReptiFiles, reptifiles.com, no date. Source for the prey weight rule: a meal should weigh 10–15% of the snake’s body weight.

_Educational resource, not veterinary advice. PetGuideCalc — https://petguidecalc.com_