PVR calculator
With 400 mL in the bladder before voiding, 350 mL passed and 50 mL left behind, the residual ratio is 12.5% and voiding efficiency 87.5%. Enter the three volumes in millilitres, and they must add up. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Pre void volume
- 400
- Voided volume
- 350
- Residual volume
- 50
- Pvr ratio
- 12.5 percent
- Voiding efficiency
- 87.5
- Volume unit
- mL
Post-void residual volume is the urine remaining in the bladder after a void. Clinics, urodynamic reports, and teaching labs routinely turn that leftover millilitres into two complementary percentages: the PVR ratio, residual divided by pre-void volume, and voiding efficiency, voided volume divided by the same pre-void volume. This calculator accepts three finite millilitre readings—pre-void bladder volume, voided volume, and post-void residual—checks that pre-void equals voided plus residual, and returns both percentages with the echoed volumes and a readable formula.
What post-void residual ratio and voiding efficiency measure
After a person voids, a residual volume of urine can remain in the bladder. Clinicians and students measure that leftover with a bladder scanner, ultrasound, or catheterization and then compare it with the volume that was present just before the void. Two percentages make that comparison portable across different bladder sizes.
The post-void residual ratio, sometimes called residual fraction or PVR percent, is residual volume divided by pre-void bladder volume, multiplied by one hundred. Voiding efficiency, also called bladder voiding efficiency, is voided volume divided by the same pre-void volume, multiplied by one hundred. When the three millilitre readings are consistent, those two percentages add to one hundred: a residual ratio of twelve point five percent is the complement of an eighty-seven point five percent voiding efficiency.
This capability implements exactly those two closed-form ratios. It does not estimate volumes from ultrasound dimensions, does not apply nomograms by age or sex, and does not diagnose obstruction, infection, or retention. Pre-void volume must be strictly positive so the ratios are defined.
Residual and voided volumes must be finite and non-negative, including zero when the bladder emptied completely or when no urine was passed. The conservation identity is enforced rather than assumed: pre-void volume must equal voided volume plus residual volume, within a tiny floating-point tolerance, because a ratio built from mismatched scans is not a measurement, it is a transcription error.
Always frame the percentages as educational arithmetic from the published identities, not as a clinical diagnosis or a substitute for professional judgment, continuous monitoring, or local treatment protocols that this calculator does not collect.
Where a PVR percentage calculator is used, pricing, and limits
Urology clinics, urodynamic labs, and nursing education programs record pre-void scans, voided cups, and post-void residuals on the same worksheet and then need percentages that every trainee can recompute by hand. Courseware authors use it so homework keys match the same two formulas regardless of spreadsheet rounding. Simulation and electronic worksheet products call it so every language in a stack does not reimplement the conservation check.
Research assistants labelling synthetic voiding datasets need a deterministic reject path when the three volumes are inconsistent, because silent renormalization would hide data-entry bugs. Practical bounds keep classroom and consumer inputs sane: volumes from zero through ten thousand millilitres, with pre-void strictly positive. If your form collects ounces or cubic centimetres labelled differently, convert to millilitres first and send the millilitre numbers here.
Always present results as educational percentages from the published identities, not as a diagnostic medical device; people with urinary symptoms, known retention, or catheter plans should follow professional medical advice rather than any single automated ratio. If you later need uroflow peak rate, bladder capacity from ultrasound diameters, or creatinine-based kidney estimates, treat those as separate search intents rather than overloading this post-void residual landing.
Keep requests small, pin the rounded percentages in tests, and you get reproducible PVR ratio and voiding efficiency figures for homework, LMS plugins, and edge workers without standing up a clinical information system of your own.
What you can do with it
Urodynamic and bladder-scan worksheets
Turn a pre-void scan, a voided cup, and a post-void residual into PVR ratio and voiding efficiency percentages that match hand arithmetic.
Simulation labs and education apps
Give every client the same conservation-checked percentages instead of re-coding residual fraction in each language of a stack.
FAQ
How is voiding efficiency calculated?
When the volumes conserve, PVR ratio plus voiding efficiency equals one hundred percent.
What happens if pre-void volume does not equal voided plus residual?
The calculator does not invent a ratio from inconsistent scans, and the failed call is not billed.
How is the post-void residual ratio calculated?
Divide the residual volume by the bladder volume before voiding and multiply by 100. For example, 50 mL left out of 400 mL gives a residual ratio of 12.5%.
Why do the two percentages always add up to 100?
Because the volume before voiding is exactly what was passed plus what remained. A residual ratio of 12.5% therefore goes with a voiding efficiency of 87.5%, and a complete emptying gives 0% and 100%.
Does a high residual ratio mean urinary retention?
Not on its own. The calculator only does the arithmetic: it does not diagnose obstruction, infection or retention, and it does not compare your result with norms for age or sex. A clinician interprets the numbers.
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/pvr \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"pre_void_volume":400,"voided_volume":350,"residual_volume":50}'const res = await fetch("https://api.kit.forhosting.com/health/pvr", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"pre_void_volume": 400,
"voided_volume": 350,
"residual_volume": 50
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/pvr",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"pre_void_volume": 400,
"voided_volume": 350,
"residual_volume": 50
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/pvr", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"pre_void_volume":400,"voided_volume":350,"residual_volume":50}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"pre_void_volume":400,"voided_volume":350,"residual_volume":50}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/pvr", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"pre_void_volume": 400,
"voided_volume": 350,
"residual_volume": 50
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.pvr",
"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.
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
When the three numbers do not add up, the task fails with invalid_input instead of inventing a ratio from inconsistent scans. Successful API calls use the published $0.002 per item; invalid input is not billed.
What post-void residual ratio and voiding efficiency measure
Identical inputs always produce identical JSON because the path is pure arithmetic with no network, no model, no random seed, and no wall clock.
Input contract, conservation check, and response fields
Send three required fields as finite numbers in millilitres. Negative volumes fail because a negative millilitre reading is not a valid bladder or voided volume for this calculator. A zero pre-void volume fails because the percentages would require division by zero. A classic example is four hundred millilitres pre-void, three hundred fifty voided, and fifty residual, which yields a twelve point five percent residual ratio and an eighty-seven point five percent voiding efficiency. A complete empty with three hundred, three hundred, and zero yields a zero percent residual ratio and one hundred percent voiding efficiency. Practical bounds keep classroom and consumer inputs sane: volumes from zero through ten thousand millilitres, with pre-void strictly positive. The field pre_void_volume is the bladder volume immediately before the void and must be strictly greater than zero; aliases prevoid, pre_void, bladder_volume, pre_volume, and prevoid_volume are accepted. The field voided_volume is the urine collected during the void and must be finite and non-negative, including zero; aliases voided, void_volume, vv, and voided_vol are accepted. The field residual_volume is the post-void residual in the same unit and must also be finite and non-negative, including zero when emptying is complete; aliases pvr, post_void_residual, residual, post_void, pvr_volume, and residual_vol are accepted. Missing fields, empty strings, non-numeric text, NaN, and Infinity fail with invalid_input naming the field. After the three numbers parse, the engine checks conservation: pre_void_volume must equal voided_volume plus residual_volume within one millionth of a millilitre so floating-point noise does not reject exact sums. When that identity fails, the task returns invalid_input with a message that pre-void volume does not equal voided volume plus residual volume, and the call is not billed. On success the JSON echoes the cleaned volumes, reports pvr_ratio as residual divided by pre-void times one hundred, reports voiding_efficiency as voided divided by pre-void times one hundred, sets unit to percent and volume_unit to mL, and includes formula and method strings for display and for pinning in tests. Pricing for successful API calls is the published $0.002 per item; validation failures do not consume prepaid balance.
Where a PVR percentage calculator is used, pricing, and limits
This endpoint is that arithmetic oracle: it does not replace a bladder scanner, a uroflowmeter, or a clinician, and it does not interpret whether a residual is concerning for a given age or sex. Successful API calls cost the published $0.002 per item; validation failures, including conservation mismatches, do not consume prepaid balance.
Integration use cases
Nursing and urology homework keys
Pin expected JSON for textbook millilitre triples, including the invalid_input path when the three volumes do not add up.
Technical questions
How is the post-void residual (PVR) ratio calculated?
PVR ratio (%) = residual_volume / pre_void_volume × 100. Send the three millilitre fields; the response includes pvr_ratio and a readable formula string.
Which units should I use?
Send all three volumes in millilitres (mL). Percentages are returned in the unit field set to percent, with volume_unit set to mL.
What does the PVR calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.