Porosity from void ratio calculator
A void ratio of 0.8 gives a porosity of 0.444, about 44.4 percent voids, from n = e/(1+e). Enter either phase ratio and get the other back, with the substitution shown so a reviewer can check it. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Void ratio
- 0.8
- Porosity
- 0.4444444444
- Porosity percent
- 44.4444444444
- Direction
- void_ratio_to_porosity
- Source
- void_ratio
Geotechnical engineers, foundation designers, and soil-mechanics students constantly convert a laboratory void ratio into porosity, or porosity back into void ratio, when they close a phase diagram, check a compaction report, or turn a textbook identity into a number they can put on a drawing. Void ratio e is the volume of voids divided by the volume of solids. Porosity n is the volume of voids divided by the total volume. Those two phase quantities are not independent: they obey the exact reciprocal identities n = e / (1 + e) and e = n / (1 − n).
What void ratio and porosity mean, and why n = e / (1 + e)
A soil element is a three-phase mixture of solids, water, and air. The solids occupy volume Vs. The total volume is V = Vs + Vv.
Void ratio e is defined as Vv divided by Vs. It is dimensionless and, for a real packing of grains, non-negative; a negative void ratio would mean a negative void volume, which no phase diagram can draw. Porosity n is defined as Vv divided by the total volume V.
It is therefore a fraction of the whole specimen, always between zero inclusive and one exclusive for a soil that still has solids. Substitute V = Vs + Vv into the definition of n and divide numerator and denominator by Vs: n equals (Vv/Vs) over (1 + Vv/Vs), which is exactly e / (1 + e). Invert the same algebra and you recover e = n / (1 − n).
Those two identities are the entire engine of this calculator. They do not depend on water content, degree of saturation, or specific gravity; they are purely volumetric. A void ratio of zero is a solid block with no pores.
The capability does not estimate e from dry density and Gs, does not convert water content to saturation, and does not classify soil type. Provide the known phase ratio and receive the other, with the formula restated so a reviewer can see the substitution.
When converting void ratio to porosity helps
Site-investigation notebooks and laboratory information systems already store void ratio from phase calculations on a measured dry density and specific gravity; they still need porosity for compressibility comments, seepage estimates, and client tables that prefer n or n percent. Soil-mechanics courses use a porosity from void ratio calculator so learners can check textbook conversions for loose sand, dense sand, and clay without standing up a spreadsheet that silently treats forty as a fraction.
Compaction and oedometer reports often quote e at a given effective stress; converting to n lets a drainage or void-volume paragraph stay consistent with the phase diagram on the same page. Research pipelines that batch thousands of specimens need fixed twelve-decimal rounding and a hard rejection of negative or non-numeric e they can assert in tests.
What you can do with it
Laboratory phase-diagram close-out
Turn a measured void ratio from dry density and Gs into porosity (and n percent) so the phase diagram, compressibility note, and client table quote the same n = e/(1+e).
Classroom and exam checks
Let students verify n from e and e from n against the reciprocal identities, including the hard reject of a negative or non-numeric void ratio.
Site-investigation notebooks
Convert rows of laboratory e values into porosity for seepage, compaction, and foundation comments without a one-off spreadsheet formula.
FAQ
How do I convert porosity back to void ratio?
Send porosity n as a fraction in [0, 1), for example 0.40 for forty percent. Do not send 40; that is not a valid fraction.
What happens if the void ratio is negative or not a number?
A negative void ratio is unphysical (Vv/Vs cannot be negative), and a non-numeric value cannot be coerced to a finite e. Failed validation is not billed.
Should I enter porosity as 40 or 0.40?
Enter 0.40 for forty percent. Porosity is a fraction of the total volume, so a value of 40 is rejected because it would mean a porosity of one hundred percent or more.
Why can porosity never reach one?
A porosity of one would mean the specimen has no solids at all, which needs an infinite void ratio. The calculator rejects that case instead of returning infinity, so porosity stays between zero and just under one.
What void ratios are typical for soils?
Laboratory sands usually sit around 0.5 to 0.8, with 0.8 a common loose-to-medium sand value. Soft clays and peats can go above 2, which corresponds to porosities well over half the volume.
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/earth/porosity-from-void-ratio \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"void_ratio":0.8}'const res = await fetch("https://api.kit.forhosting.com/earth/porosity-from-void-ratio", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"void_ratio": 0.8
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/earth/porosity-from-void-ratio",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"void_ratio": 0.8
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/earth/porosity-from-void-ratio", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"void_ratio":0.8}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"void_ratio":0.8}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/earth/porosity-from-void-ratio", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"void_ratio": 0.8
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "earth.porosity_from_void_ratio",
"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
This porosity from void ratio calculator applies those identities deterministically, returns both the dimensionless void ratio and the porosity as a fraction and as a percent, and fails with invalid_input when the void ratio is negative or non-numeric instead of inventing a silent NaN.
What void ratio and porosity mean, and why n = e / (1 + e)
Everything that is not solid is void: Vv is the sum of the water and air volumes. A void ratio of 0.80 is a common loose-to-medium sand value and maps to n = 0.80 / 1.80 ≈ 0.444, or about 44.4 percent voids. Porosity cannot reach one because that would require zero solids and an infinite void ratio, which this endpoint rejects rather than returning Infinity. Typical laboratory sands sit near e = 0.5 to 0.8; soft clays and peats can exceed e = 2. Use n as a fraction in [0, 1) or read porosity_percent when a report wants forty percent instead of 0.40.
Input contract, response shape, and error behaviour
Send 0.40 when you mean forty percent, not the integer 40 — a value of 40 is rejected as a porosity of one hundred percent or more. Failed validation is not billed. POST a JSON body with at least one of void_ratio or porosity. void_ratio is the dimensionless phase ratio e = Vv/Vs; accepted aliases are e, void, voidRatio, and e_ratio. porosity is the dimensionless fraction n = Vv/V in the half-open interval from zero inclusive to one exclusive; accepted aliases are n, poro, n_e, and porosity_frac. Each field may arrive as a JSON number or as a numeric string. Missing both fields fails with invalid_input naming the pair. A void ratio that is empty, infinite, or otherwise non-numeric fails with invalid_input and a message that the value must be a finite number. A strictly negative void ratio is unphysical and is rejected with invalid_input rather than producing a negative porosity that would look like a number and be wrong. Porosity below zero or at or above one is likewise rejected: n = 1 would make e = n/(1−n) undefined. When both fields are supplied, void_ratio is the source of truth and porosity is recomputed from n = e/(1+e), so a stale companion value cannot silently disagree with the identity. On success the body echoes rounded void_ratio and porosity, reports porosity_percent as one hundred times n, restates formula and equation, names direction as void_ratio_to_porosity or porosity_to_void_ratio, names source, method phase_relationship, unit labels, and a short steps array for teaching UIs. Example: void_ratio equals 0.8 yields porosity 0.4444… and porosity_percent 44.44…. Values are rounded to twelve decimal places so Worker and browser JSON match. Successful analytic calls use the published $0.002 base price with no model tokens and no outbound network.
Where a porosity-from-void-ratio API earns its keep
A tiny parse API applies the same identity every time and avoids the off-by-one of writing n = e/(1−e) by habit from a neighbouring formula.
Technical questions
How do I convert a soil void ratio to porosity?
Send void_ratio e (or alias e / void). The API returns porosity n = e / (1 + e) as a fraction and porosity_percent as 100 n. Example: e = 0.8 gives n ≈ 0.4444 (44.44%).
Why is a porosity of 1 (one hundred percent) rejected?
n = 1 means the specimen has no solids, so e = n/(1−n) is undefined. The handler rejects n ≥ 1 instead of returning Infinity.
What does the porosity from void ratio calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.