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Dehydration Percentage Calculator

Work out dehydration percentage instantly with clear inputs, formula shown and shareable results.

About Dehydration Percentage Calculator

Compares current weight with a known pre-illness weight; each kilogram lost represents about one litre of fluid deficit.

Formula

Dehydration from weight change

Dehydration (%) = (pre-illness weight - current weight) / pre-illness weight x 100; deficit (mL) = weight lost (kg) x 1000

Worked example

With the default values below, Dehydration Percentage Calculator returns Dehydration of 6.7%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Weight before illnessaccepts 1–150 kg
12 kg
Current weightaccepts 1–150 kg
11.2 kg

Results

Dehydration
6.7%
Fluid deficit
800 mL
Severity band
Moderate dehydration (5-9%)

Step by step

  1. 1Values used
  2. 2Dehydration from weight change
  3. 3Dehydration= 6.7
  4. 4Fluid deficit= 800 mL
  5. 5Severity band= Moderate dehydration (5-9%)

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

What if the previous weight is unknown?

Clinical signs are used instead, which are less precise; weight change remains the reference standard.

How fast should the deficit be replaced?

Usually over 24 to 48 hours alongside maintenance fluids, faster only in shock.

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