What is the difference between RER and MER?

RER (Resting Energy Requirement) is the energy needed at rest in a thermoneutral environment. MER (Maintenance Energy Requirement) adjusts RER by a maintenance factor to account for activity, life stage, illness, or hospitalization.

When should I recalculate RER?

Recalculate RER whenever body weight changes significantly, especially in growing animals, hospitalized patients, or during weight-loss programs. Weekly rechecks are common in acute settings.

Can I use this calculator for exotic species?

This calculator uses the 70 × (BW kg)^0.75 formula commonly applied to dogs and cats. Exotic species often require species-specific equations and should not rely on this tool.

Clinical decision support

Resting energy requirement calculator

Calculate RER and optional MER for dogs and cats. Adjust formula constants and maintenance factors, review interpretation cues, and check suggested next clinical steps. Educational decision-support tool only.

Species Body weight

Unit Maintenance factor

Educational support only. Verify with clinical judgment.

Formula constants & custom factor

RER constant RER exponent

Custom factor (overrides select if >0)

Defaults are commonly cited references. Adjust to match your protocol. Preset factors: RER 1.0, Neutered 1.2, Intact 1.4, Light work 1.6, Moderate work 1.8, Heavy work 2.0, Weight loss 0.8, Hospitalized 1.3, Medical illness 1.5, Severe illness 1.7, Growing 1.8.

RER

— kcal/day

Enter weight

Enter weight to calculate RER.

Adjusted energy target —

—

Factor —

Select a maintenance factor.

Interpretation —

—

Clinical next steps

Assess current body condition score (BCS) and muscle condition.
Consider disease state: renal, hepatic, cardiac, or neoplastic conditions may alter targets.
Schedule recheck weight every 3–7 days in hospitalized patients; every 2–4 weeks for outpatients.
Avoid overfeeding in critical care; refeeding syndrome risk is real in malnourished patients.
Confirm food caloric density and feeding route (oral, tube, parenteral) before prescribing volumes.

Safety checks

This tool supports calculation and education only.
It does not diagnose, prescribe, or replace current clinical references.
Verify patient-specific decisions with current formularies, hospital protocols, and veterinarian judgment.
Confirm weight units and reassess as body weight changes.
Maintenance factors are general estimates; adjust to individual patient response and body condition.

Basis and limits

Calculation basis: RER = constant × (body weight in kg)^exponent. MER = RER × maintenance factor. Defaults: constant 70, exponent 0.75.
Scope: this tool provides a quick energy starting point. It does not select therapeutic diets or medical feeding protocols.
Before use: confirm weight, body condition, and clinical status. Adjust for obesity, pregnancy, or severe disease.
Maintenance factors: typical ranges vary by source. Verify factors against your preferred nutrition reference.

Formula audit trail

Calculation steps will appear here for verification.

Resting energy requirement calculator

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