Resting Energy Requirement (RER) is the number of calories a cat needs at complete rest to maintain basic body functions such as circulation, respiration, and thermoregulation. It is calculated as RER = 70 × (body weight in kg)^0.75 — the same formula used in most veterinary nutrition textbooks.

Maintenance Energy Requirement (MER) is RER multiplied by a life-stage or condition factor that accounts for activity, reproductive status, growth, or weight management goals. For example, an intact adult cat has MER = RER × 1.4, while a neutered adult uses × 1.2.

Are these multipliers exact?

The multipliers are widely accepted clinical guidelines from WSAVA and AAFP, but individual cats vary. Body condition score (BCS) should guide adjustments — if a cat gains weight, reduce calories 10–20%; if it loses weight unintentionally, increase calories or investigate medical causes.

How do I convert kcal/day to cups of food?

Divide the cat's daily MER by the caloric density of the food (kcal/cup for dry food, kcal/can for wet food). This information appears on the pet food label or the manufacturer's website.

Should I use RER or MER to feed my cat?

Use MER for healthy cats at home. RER is used in clinical settings (hospitalized, post-operative, critically ill patients) where activity is essentially zero. Feeding a healthy cat only at RER will lead to underfeeding over time.

Does this tool store any data?

No. All calculations run in your browser. Nothing is sent to or stored on any server.

Cat Calorie & RER Calculator

Enter your cat's weight and life stage to get resting energy requirement (RER) and total daily calorie needs.

Cat Details

Body Weight

Life Stage / Condition

Multipliers per WSAVA/AAFP nutritional guidelines.

Results

Enter a weight and press Calculate to see results.

RER Quick Reference (neutered adult)

Weight (kg)	Weight (lbs)	RER (kcal/day)	MER neutered (kcal/day)

Summary

This tool calculates a cat's Resting Energy Requirement (RER) using the standard veterinary formula RER = 70 × (body weight in kg)^0.75, then applies a life-stage multiplier recommended by WSAVA and AAFP guidelines to estimate total daily calorie needs. Enter weight in kilograms or pounds and select the cat's life stage to see RER and Maintenance Energy Requirement (MER) in kilocalories per day.

How it works

Enter the cat's current body weight.
Select the weight unit (kg or lbs).
Choose the life stage or condition that best describes the cat.
Click Calculate to see RER and daily MER in kcal/day.
Use the result to determine how much food to feed based on the food's caloric density (kcal/cup or kcal/can shown on the label).
Recheck weight monthly and recalculate — energy needs change with body condition.

Use cases

Determine how many calories a healthy adult cat needs per day.
Calculate kitten energy requirements during rapid growth.
Adjust feeding for an overweight cat following a weight-loss multiplier.
Estimate post-surgery or illness recovery calorie targets.
Compare calorie needs before and after spay or neuter.
Help clients understand why cat food label feeding guides are weight-based.
Teach veterinary students the standard RER formula and multipliers.
Plan a feeding schedule when transitioning between food brands.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu