Plasma volume
An 80 kg man who is 180 cm tall with a hematocrit of 0.45 has just under 3 litres of plasma, out of a little over 5 litres of blood. Enter weight, height, sex and hematocrit to get the split. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Weight
- 80
- Height
- 180
- Sex
- Male
- Hematocrit
- 0.45
- Weight (kg)
- 80 L
- Height (cm)
- 180
- Height m
- 1.8
- Blood volume l
- 5.3190608
Plasma volume is the liquid fraction of circulating blood that remains after hematocrit accounts for packed cells. This plasma volume calculator estimates that volume in liters from body weight in kilograms, standing height in centimetres, biological sex, and hematocrit as a decimal fraction using the Nadler blood-volume method, then multiplying by one minus hematocrit. Weight, height, and sex feed the 1962 Nadler equations that predict whole-blood volume in liters; hematocrit then splits that volume into plasma and red-cell compartments. Hematocrit must lie between 0 and 1 inclusive: a value such as 45 is rejected instead of being treated as a percentage, which keeps the contract unambiguous for scripts and forms.
Nadler plasma volume explained, with the full result
Plasma is the aqueous matrix of blood that carries proteins, electrolytes, clotting factors, and dissolved gases around the body. Its volume is not the same as whole-blood volume: hematocrit is the fraction of packed cells, so plasma volume equals blood volume times one minus hematocrit. Direct measurement of plasma volume uses tracer dilution, which is impractical for a homework check or a planning spreadsheet.
The Nadler method, published in 1962, estimates whole-blood volume from standing height in metres, body weight in kilograms, and sex with two linear-plus-cubic formulas. For males, blood volume in liters is 0.3669 times height in metres cubed plus 0.03219 times weight in kilograms plus 0.6041. For females, blood volume in liters is 0.3561 times height in metres cubed plus 0.03308 times weight in kilograms plus 0.1833.
This calculator accepts height in centimetres, converts to metres internally, applies the matching Nadler coefficients, then returns plasma volume in liters as blood volume times one minus hematocrit. It also reports the intermediate blood volume and the complementary red-cell volume so you can audit the split. The result is an anthropometric estimate, not a measured compartment: it does not replace isotope or dye dilution, does not adjust for pregnancy, altitude, or hemorrhage, and does not issue a clinical decision.
Use it when you already have weight, height, sex, and a hematocrit fraction and need a reproducible liter figure for education, software tests, or planning notes.
Input contract, hematocrit range, and error behaviour
Sex accepts male, female, m, f, man, woman, and their plural forms after case folding so forms and spreadsheets can reuse the same contract. Weight and height must be strictly positive and within the documented ceilings of five hundred kilograms and three hundred centimetres. Hematocrit must be between 0 and 1 inclusive.
Sending 45, 1.2, or a negative fraction is rejected so a unit mix-up cannot invent liters of plasma. A typical check is an eighty kilogram man at one hundred eighty centimetres with hematocrit 0.45. Failed validation is not billed.
When a plasma volume estimate is useful
Physiology and nursing courses use a plasma volume calculator so learners can check Nadler arithmetic and the hematocrit split without a spreadsheet that silently accepts a percentage. Product teams call the same contract from scripts to seed test vectors for fluid-balance dashboards, to normalize user-entered anthropometrics before a chart, or to satisfy programming-challenge statements that demand a Nadler estimate rather than a black-box app. Treat the output as an educational and planning estimate: if clinical or research accuracy is required, prefer measured plasma volume and a qualified professional.
Keep units honest so kilograms, centimetres, and a 0–1 hematocrit fraction are never mixed with pounds, inches, or a percentage by accident.
What you can do with it
Physiology and nursing homework
Students enter weight, height, sex, and a hematocrit fraction from a case vignette and compare hand-written Nadler plasma volume against a deterministic liter result.
Planning notes before tracer studies
Notebooks compute an anthropometric Nadler prior in liters from known size and hematocrit without standing up a clinical dosing system.
FAQ
How is plasma volume calculated from the Nadler method?
Blood volume is estimated with the 1962 Nadler equations from height in metres, weight in kilograms, and sex. Plasma volume in liters is then blood volume times (1 minus hematocrit), where hematocrit is a fraction between 0 and 1.
What happens if hematocrit is not between 0 and 1?
Hematocrit must be a fraction such as 0.45, not a percentage such as 45. Values below 0 or above 1 are rejected and not billed.
Which units should I send for weight and height?
Weight in kilograms and height in centimetres. Height is converted to metres inside the Nadler formula. Convert from pounds or inches before calling so the published coefficients apply correctly.
Does this replace a measured plasma volume?
No. Nadler is an anthropometric estimate from weight, height, sex, and hematocrit. Use tracer dilution and a qualified professional when clinical or research accuracy is required.
Does the estimate adjust for pregnancy, altitude or blood loss?
No. It is an anthropometric estimate built only from weight, height, sex and hematocrit. It does not adjust for pregnancy, altitude or hemorrhage, and it does not replace a tracer dilution measurement.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/plasma-volume \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"weight":80,"height":180,"sex":"male","hematocrit":0.45}'const res = await fetch("https://api.kit.forhosting.com/health/plasma-volume", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"weight": 80,
"height": 180,
"sex": "male",
"hematocrit": 0.45
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/plasma-volume",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"weight": 80,
"height": 180,
"sex": "male",
"hematocrit": 0.45
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/plasma-volume", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"weight":80,"height":180,"sex":"male","hematocrit":0.45}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"weight":80,"height":180,"sex":"male","hematocrit":0.45}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/plasma-volume", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"weight": 80,
"height": 180,
"sex": "male",
"hematocrit": 0.45
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.plasma_volume",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_weight_kg | 500 |
max_height_cm | 300 |
hematocrit_min | 0 |
hematocrit_max | 1 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Successful API calls are billed at $0.002; invalid input is not charged.
Input contract, hematocrit range, and error behaviour
POST a JSON body with four required fields: weight in kilograms (aliases mass, kg, weight_kg, w), height in centimetres (aliases height_cm, h, stature), sex for the Nadler coefficient set, and hematocrit as a fraction between zero and one (aliases hct, hct_frac, pcv). Each numeric field may arrive as a JSON number or as a numeric string; missing fields, empty strings, and non-finite values fail with invalid_input naming the field. That rule is the one people miss: laboratory printouts often show hematocrit as a percentage such as forty-five, but this endpoint will not divide by one hundred for you. On success the body echoes weight_kg, height_cm, height_m, sex, and hematocrit; reports blood_volume_l, plasma_volume_l (also as plasma_volume), and red_cell_volume_l; and tags unit as L, method as nadler, plus a formula string for the chosen sex. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing Nadler coefficients yourself.
Where a plasma volume API earns its keep
Exam-prep generators need a deterministic oracle that marks hematocrit outside 0 to 1 as invalid_input instead of inventing a volume from a unit error. Research notebooks sometimes need a quick anthropometric prior before a tracer study is even scheduled; this endpoint returns liters and the intermediate blood volume so those notes stay auditable. On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result.
Integration use cases
Deterministic test fixtures
Generate reproducible plasma, blood, and red-cell volume fields plus deliberate hematocrit-out-of-range rejections for unit tests and CI assertions.
Technical questions
What does the plasma volume calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.