pH from pOH calculator
A pOH of 4 means a pH of 10, a basic solution at 25 °C: enter the pOH and get the pH as 14 minus pOH, with an acidic, neutral or basic label and each substitution step. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Solution pOH
- 7
- POH
- 7
- Ph
- 7
- PH
- 7
- Creativity
- 25 °C
A pH from pOH calculator converts the hydroxide scale into the acidity number every lab notebook and exam expects. Enter a finite solution pOH and the tool returns pH equals fourteen minus that pOH at standard temperature about twenty-five degrees Celsius, where the water ion product makes pH plus pOH equal fourteen. You also get a short acidity label—acidic, neutral, or basic—and step-by-step substitution you can paste into homework or automated tests. Students checking titration math, technicians reconciling meter pOH with report pH, and graders asserting known pairs all need that closed relation without a spreadsheet.
What pH and pOH mean at standard temperature
pH and pOH are complementary logarithmic scales for aqueous acidity and basicity. By definition, pH is the negative base-ten logarithm of hydrogen ion activity, often approximated with concentration, and pOH is the analogous measure for hydroxide. At standard classroom temperature near twenty-five degrees Celsius, the ion product of pure water is about one times ten to the minus fourteen, which forces the simple relation pH plus pOH equals fourteen.
Rearranged, pH equals fourteen minus pOH. When pOH is seven, pH is also seven and the solution is neutral on that reference scale. When pOH is less than seven, hydroxide is relatively high, pH is greater than seven, and the solution is basic.
When pOH is greater than seven, the solution is acidic on the pH scale. The same arithmetic works for values outside the familiar zero-to-fourteen band when activity or concentration definitions allow extreme logs; what never works is a non-numeric pOH, because subtraction from fourteen is only defined for finite numbers. Teachers and automated graders care about that rejection as much as the happy path: a silent fallback would hide a data-entry error.
The check path recomputes fourteen minus the published pOH with the same fixed rounding used for the ph field, so a successful response always ships with steps you can assert in tests or lab notebooks. Related tasks such as converting [H+] or [OH−] into scale values, buffer Henderson–Hasselbalch pH, or temperature-corrected Kw are intentionally out of scope here so this landing stays focused on the single search intent of converting a known pOH into pH at standard temperature.
Practical tips, limits, and related searches
Keep pOH inside the published absolute range so fourteen minus pOH cannot overflow into a non-finite pH the solver must reject. Use the standard-temperature relation only when Kw is taken as one times ten to the minus fourteen; if your lab works far from twenty-five degrees Celsius and you need temperature-corrected Kw, apply that correction outside this tool and do not expect this landing to recompute the ion product.
Prefer this capability when you already know pOH and only need pH; if your source is only [OH−], compute pOH first with a dedicated concentration tool, then convert. Round-trip intuition is easy: fourteen minus the published pH recovers the original pOH within the same twelve-decimal rounding for typical aqueous values, and confirming acidity flips correctly when you move pOH across the pure-water reference of seven.
What you can do with it
Lab notebook conversion of meter pOH
Technicians convert a reported pOH into pH for forms and LIMS fields that only accept the pH scale at standard temperature.
FAQ
What happens if pOH is non-numeric?
pH cannot be computed from a missing, blank, letter, or non-finite pOH.
Does this calculate pOH from [OH−] or buffer pH?
No. It only converts a known pOH into pH at the standard 14 relation. Use a dedicated concentration or buffer tool if you need those models.
Is the pH from pOH calculator free?
The browser tool is free and runs locally.
How do I calculate pH from pOH?
Subtract the pOH from 14. A pOH of 3, for example, gives a pH of 11. This works because pH and pOH add up to 14 at about 25 °C, where the ion product of water is 1 × 10⁻¹⁴.
Does it work far from 25 °C?
No. The calculator always uses the standard-temperature relation in which pH and pOH add up to 14. If your sample is far from 25 °C and you need a temperature-corrected value, apply that correction separately.
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/chem/ph-from-poh \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"poh":7}'const res = await fetch("https://api.kit.forhosting.com/chem/ph-from-poh", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"poh": 7
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/chem/ph-from-poh",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"poh": 7
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/chem/ph-from-poh", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"poh":7}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"poh":7}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/chem/ph-from-poh", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"poh": 7
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "chem.ph_from_poh",
"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_abs | 1000000000000 |
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
Non-numeric pOH is rejected with a clear invalid_input error so a blank cell, a letter, or a non-finite token never silently produces a wrong acidity.
How to call the API and what comes back
The value must be a genuine finite number; missing fields, empty strings, letters, mixed tokens, NaN, and Infinity are all non-numeric and rejected. Send a JSON body with one required finite number: poh (aliases pOH, p_oh, poH, oh_scale). Absolute value must stay within the published limit of one trillion so intermediate results remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes rounded poh and pOH, ph and pH to the same rounded value fourteen minus pOH, formula to the string pH equals fourteen minus pOH, temperature to twenty-five degrees Celsius, relation to pH plus pOH equals fourteen, acidity to acidic, neutral, or basic, message to a short English summary, and steps to an ordered array of substitution lines. Failed validation—missing poh, non-numeric input, values outside absolute limits, or a non-finite computed pH—returns invalid_input and is never charged. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price. Prefer sending numeric JSON rather than pre-formatted strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern including optional scientific notation for values such as one e minus one.
Practical tips, limits, and related searches
When teaching, pair classic examples: pOH equals seven yields pH seven and neutral; pOH equals three yields pH eleven and basic; pOH equals ten yields pH four and acidic; and a non-numeric string such as not-a-number demonstrates the hard invalid_input path. This landing targets people searching for a pH from pOH calculator, fourteen minus pOH, or pH plus pOH equals fourteen online; it is not a pOH-from-hydroxide calculator, not a pH-from-hydrogen-ion calculator, and not a buffer or titration curve tool. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send garbage tokens.
Integration use cases
Homework checks for pH = 14 − pOH
Students enter textbook pOH values and compare hand-written pH and acidity labels against a deterministic result before submitting.
Unit tests for chemistry helpers
Generate known-good acidic, neutral, and basic pH cases from pOH plus deliberate non-numeric rejections for coding kata and grading pipelines.
Technical questions
How do you calculate pH from pOH?
At standard temperature (~25 °C), use pH = 14 − pOH because pH + pOH = 14. This tool returns the rounded pH, acidity class, and substitution steps.
What pOH gives pH 7?
At the pure-water reference, pOH = 7 gives pH = 7 and acidity neutral.