# Blood Volume Calculator

> Estimates total blood volume from sex, height and weight with the Nadler (1962) equation, or from weight and body build with Gilcher's rule of fives (mL/kg), and splits it into plasma and red cell volume when the haematocrit is given.

- Calculator id: `blood-volume` · Category: Medical & Clinical (`medical`) · Tool name: `estimate_blood_volume`
- Canonical page: https://tttkmbb.com/medical/blood-volume · This document: https://tttkmbb.com/medical/blood-volume.md · JSON definition: https://tttkmbb.com/medical/blood-volume.json

## Purpose

Estimates total blood volume from sex, height and weight with the Nadler (1962) equation, or from weight and body build with Gilcher's rule of fives (mL/kg), and splits it into plasma and red cell volume when the haematocrit is given.

**Use when:** You need an adult's estimated total blood volume (L, mL or mL/kg) or plasma volume, for example to express blood loss as a fraction of volume or to plan apheresis or plasma exchange.

**Do not use when:** The person is a child or neonate (paediatric mL/kg norms differ), pregnant, or has extreme body composition; measured (isotope-dilution) volumes are needed for dosing decisions. Results are informational and not medical advice.

## Input

| Parameter | Type | Unit | Required | Description |
| --- | --- | --- | --- | --- |
| `sex` | enum: male \| female |  | required | Sex used to select the formula coefficients or thresholds. |
| `height_cm` | number | cm | required | Height in centimetres (used by the Nadler equation). (min 100, max 250) |
| `weight_kg` | number | kg | required | Body weight in kilograms. (min 20, max 400) |
| `method` | enum: nadler \| gilcher_rule |  | optional, default "nadler" | Estimation method; Gilcher's rule uses weight and build only. |
| `build` | enum: athletic \| normal \| thin \| obese |  | optional, default "normal" | Body build used only by Gilcher's rule; ignored by Nadler. |
| `hematocrit_percent` | number | % | optional | Optional haematocrit in percent; enables plasma and red cell volume. (min 10, max 70) |

## Output

| Field | Type | Unit | Description |
| --- | --- | --- | --- |
| `blood_volume_l` | number | L | Estimated total blood volume in litres. |
| `blood_volume_ml` | number | mL | Same volume in millilitres. |
| `ml_per_kg` | number | mL/kg | blood_volume_ml / weight_kg (adult norms about 60–75 mL/kg). |
| `plasma_volume_ml` | number | mL | Blood volume × (1 − haematocrit); only when hematocrit_percent is given. |
| `red_cell_volume_ml` | number | mL | Blood volume × haematocrit; only when hematocrit_percent is given. |
| `method_used` | string |  | Equation or factor applied. |

## Formula

`Nadler: BV (L) = 0.3669 × h³ + 0.03219 × weight_kg + 0.6041 (male) or 0.3561 × h³ + 0.03308 × weight_kg + 0.1833 (female), h = height_cm / 100 in metres. Gilcher: BV (mL) = weight_kg × factor, factor (mL/kg) male athletic 75 / normal 70 / thin 65 / obese 60, female 70 / 65 / 60 / 55. plasma_volume_ml = BV × (1 − hematocrit_percent / 100); red_cell_volume_ml = BV × hematocrit_percent / 100`

Nadler's regression was fitted to isotope-dilution measurements in healthy adults and is the equation built into apheresis instruments; Gilcher's rule is a bedside approximation. Both assume normal hydration and typically differ by up to about 10%. Results are informational only and not a substitute for clinical judgement or medical advice.

## Data Sources

- Nadler SB, Hidalgo JU, Bloch T (1962) Prediction of blood volume in normal human adults, Surgery 51:224-232 — https://pubmed.ncbi.nlm.nih.gov/21936146/ (peer_reviewed, retrieved 2026-09-24)
- Wikipedia – Blood volume (Nadler equation, Gilcher's rule of fives) — https://en.wikipedia.org/wiki/Blood_volume (reference, retrieved 2026-09-24)

Data freshness: `static`. Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output.

## API

- `GET https://tttkmbb.com/api/v1/calculate/blood-volume?sex=…&height_cm=…&weight_kg=…`
- `POST https://tttkmbb.com/api/v1/calculate/blood-volume` with JSON body `{"inputs": {…}}`
- Response: unified envelope (`success`, `request`, `result.values`, `result.units`, `sources`, `freshness`, `timestamp`, `next_actions`, `links`); see https://tttkmbb.com/docs/response-format.md
- Schema: https://tttkmbb.com/api/v1/calculators/blood-volume · OpenAPI operationId `estimate_blood_volume` in https://tttkmbb.com/openapi.json
- Authentication: none. Rate limit: fair use, see https://tttkmbb.com/docs/rate-limits.md.

## MCP

- Server: `https://tttkmbb.com/mcp` (Streamable HTTP, JSON-RPC 2.0, no auth)
- Tool:  `run_calculator` with `{"calculator_id": "blood-volume", "inputs": {…}}`

## Example

- Male, 180 cm, 80 kg, haematocrit 45% (Nadler): inputs `{"sex":"male","height_cm":180,"weight_kg":80,"hematocrit_percent":45}` → `{"blood_volume_l":5.319,"blood_volume_ml":5319,"ml_per_kg":66.5,"plasma_volume_ml":2925,"red_cell_volume_ml":2394}`
- Female, 165 cm, 60 kg (Nadler): inputs `{"sex":"female","height_cm":165,"weight_kg":60,"method":"nadler"}` → `{"blood_volume_l":3.768,"blood_volume_ml":3768,"ml_per_kg":62.8}`

```
GET https://tttkmbb.com/api/v1/calculate/blood-volume?sex=male&height_cm=180&weight_kg=80&hematocrit_percent=45
```

## Limitations

The person is a child or neonate (paediatric mL/kg norms differ), pregnant, or has extreme body composition; measured (isotope-dilution) volumes are needed for dosing decisions. Results are informational and not medical advice. Nadler's regression was fitted to isotope-dilution measurements in healthy adults and is the equation built into apheresis instruments; Gilcher's rule is a bedside approximation. Both assume normal hydration and typically differ by up to about 10%. Results are informational only and not a substitute for clinical judgement or medical advice. All values are computed from the formula above; no measurement or live data is involved.

## FAQ

**Which method should I use?**

Nadler when height is known: it is the standard regression and what apheresis systems use. Gilcher's rule needs only weight and a build category and is a rounder estimate.

**Why is mL/kg lower in obesity?**

Adipose tissue is poorly vascularised, so blood volume rises more slowly than weight; Nadler captures this through the height term and Gilcher through the obese factor (60 / 55 mL/kg).

**How is this used for blood loss?**

Haemorrhage classes are fractions of total volume: 15% of a 5.3 L volume is about 800 mL. The estimate does not account for pregnancy, dehydration or anaemia.

## Related

- [Body Surface Area Calculator](https://tttkmbb.com/health/body-surface-area.md) — Body surface area for BSA-based apheresis and chemotherapy calculations.
- [Adjusted Body Weight Calculator](https://tttkmbb.com/medical/adjusted-body-weight.md) — Dosing weight for people well above ideal weight.
- [Parkland Formula Calculator](https://tttkmbb.com/medical/parkland-formula.md) — Fluid volumes for burn resuscitation.