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API · /samplesize-api

Sample Size API

healthy 3,896 Subscribers

Survey and poll sample-size planning as an API, computed locally and deterministically. The proportion endpoint computes the number of respondents needed to estimate a proportion within a target margin of error at a chosen confidence level, n = z²·p(1−p)/E², defaulting to the worst-case p = 0.5 that maximises the required size, with an optional finite-population correction n/(1 + (n−1)/N) for a known population — the classic ±5 % margin at 95 % confidence needs 385 responses, ±3 % needs 1 068, and capping the population at 1 000 cuts the ±5 % requirement to 278. The mean endpoint sizes a sample for estimating a mean to within a margin of error from the standard deviation, n = (z·σ/E)². The margin endpoint inverts the relationship, returning the margin of error a given sample size actually achieves. The critical z-value is computed from the confidence level with a high-accuracy inverse-normal so any confidence works, not just the textbook 90/95/99 %. Margins, proportions and confidence are decimals (0.05, 0.5, 0.95). Everything is computed locally and deterministically, so it is instant and private. Ideal for market-research, polling, UX-research, survey-platform, product-analytics and statistics-education app developers, study-planning and sample-size tools, and research software. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is sample-size planning with the normal approximation; for A/B-test significance use an A/B-test API and for descriptive statistics a statistics API.

#sample-size #survey #margin-of-error #polling #market-research #developer-tools
api.oanor.com/samplesize-api
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Machine-readable spec so AI agents can integrate this API.

/api/samplesize-api/openapi.json
/api/samplesize-api/llms.txt

Discovery: GET /api/index.json lists every API.

API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
87 ms
Server probes · 24h
Subscribers
3,896
active
Total calls
20
last 7 days
status Full status page → · 24 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 6,200 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • 6,200 calls/month
  • 2 req/sec
  • Proportion + mean + margin of error
  • No credit card
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Starter

€5.60 /month

  • 62,000 calls / month
  • 6 requests / second
  • Hard cap (429 above quota, no overage)
  • 62,000 calls/month
  • 6 req/sec
  • Any confidence level, finite population
  • Email support
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Pro

€15.80 /month

  • 280,000 calls / month
  • 15 requests / second
  • Hard cap (429 above quota, no overage)
  • 280,000 calls/month
  • 15 req/sec
  • Survey-platform & research pipelines
  • Priority support
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Mega

€49.50 /month

  • 1,550,000 calls / month
  • 40 requests / second
  • Hard cap (429 above quota, no overage)
  • 1,550,000 calls/month
  • 40 req/sec
  • Platform scale
  • Dedicated SLA
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Related APIs

Other APIs with overlapping tags.

Statistical Inference API

Inferential-statistics maths as an API, computed locally and deterministically. The samplesize endpoint computes how many respondents a survey or experiment needs for a proportion, n = Z²·p(1−p)/E², from a confidence level and a margin of error (using p = 0.5 for the most conservative size), with a finite-population correction when the population is known. The confidence endpoint builds a confidence interval for a mean (estimate ± Z·σ/√n) or a proportion (p ± Z·√(p(1−p)/n)), returning the standard error, margin of error and the lower and upper bounds. The ztest endpoint runs a one-sample z-test, z = (x̄ − μ₀)/(σ/√n), and returns the z-score, the one- or two-tailed p-value and whether the result is significant at the chosen alpha. The z-scores come from an exact inverse-normal and the p-values from the normal CDF. Everything is computed locally and deterministically, so it is instant and private. Ideal for A/B-testing, survey, research and analytics app developers, experiment dashboards and data-science tools, and education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is inferential statistics; for descriptive statistics use a statistics API and for probability distributions use a probability API.

api.oanor.com/inference-api

Equine Care API

Horse-care maths as an API, computed locally and deterministically — the everyday numbers a horse owner, barn manager or vet tech runs without reaching for a chart. The weight endpoint estimates body weight from a weight-tape measurement using the classic formula weight ≈ heart girth² × body length ÷ a type divisor (adult 330, yearling 301, weanling 280, pony 299) with measurements in inches — a horse with a 72-inch girth and 66-inch length comes out at about 1,037 lb (470 kg), the number you actually dose wormer and feed against. The feed endpoint turns body weight and a goal into daily forage: horses eat roughly 1.5–2.5 % of body weight in dry-matter forage a day, so a 1,000 lb horse on maintenance wants about 15–20 lb of hay, more to gain and less to slim. The gestation endpoint gives the foaling due date and the normal 320–362 day window from a breeding date — a mare bred on 1 April is due around 7 March the next year, give or take three weeks. Everything is computed locally and deterministically, so it is instant and private. Ideal for barn-management and horse-care apps, breeding and foaling trackers, feed-calculator and tack-shop sites, and equine-vet tools. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 compute endpoints. Educational estimates — not veterinary advice.

api.oanor.com/equine-api

Darkroom API

Analog darkroom and film maths as an API, computed locally and deterministically — the three corrections that bite when you develop film and make prints by hand. The reciprocity endpoint corrects long exposures for reciprocity failure, where film loses sensitivity past about a second: corrected time = metered^p (Schwarzschild p ≈ 1.3 for many films, settable per datasheet), so a metered 10-second exposure really wants about 20 seconds, a full stop more, while anything under the threshold is left untouched. The printexposure endpoint adjusts enlarger exposure when you change print size — light spreads as you raise the head, so exposure is proportional to (magnification + 1)², where magnification is print size ÷ negative size: going from 2× to 4× magnification turns a 10-second exposure into 27.8 seconds, about 1.5 stops, ready for f-stop printing. The pushpull endpoint scales development time for pushing or pulling film by N stops — time = base × factor^stops, roughly +40 % per stop pushed — turning a 7-minute base into 13.7 minutes at +2 stops, or 5 minutes pulled a stop. Everything is computed locally and deterministically, so it is instant and private. Ideal for film-photography and darkroom apps, light-meter and timer companions, lab and workshop tools, and analog-photography sites. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 compute endpoints. For digital depth-of-field use a photography API; for lab molarity use a dilution API.

api.oanor.com/darkroom-api

Aquascape API

Planted-aquarium and aquascaping maths as an API, computed locally and deterministically — the dosing and water numbers a high-tech planted tank runs on, not the rolls of a dice. The co2 endpoint gives the dissolved CO2 concentration from pH and carbonate hardness using the classic relationship CO2 (ppm) ≈ 3 × KH (dKH) × 10^(7 − pH), and flags it against the 15–30 ppm window plants want — at pH 6.6 and KH 4 you are at about 30 ppm, the top of the safe zone, while pH 7.0 and KH 3 is a carbon-limited 9 ppm. The fertilizer endpoint turns a dry-salt dose into the nutrient ppm it adds, the heart of Estimative Index dosing: ppm = grams × the nutrient mass fraction × 1000 ÷ tank litres, so 1 g of KNO3 in 100 litres adds 6.1 ppm nitrate and 3.9 ppm potassium, and it knows KNO3, KH2PO4, K2SO4, MgSO4 (Epsom) and Ca(NO3)2. The substrate endpoint sizes the substrate from the footprint and target depth — a 60 × 30 cm tank at 6 cm deep needs 10.8 litres, two 9-litre aquasoil bags. Everything is computed locally and deterministically, so it is instant and private. Ideal for aquascaping and planted-tank apps, fertiliser-dosing calculators, CO2-rig tools, and aquarium-shop and hobby sites. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 compute endpoints. For a tank water volume or fish stocking use an aquarium API; for pool chemistry use a pool API.

api.oanor.com/aquascape-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for Sample Size API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Sample Size API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Sample Size API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Sample Size API cost?
Sample Size API has a free tier with 100 calls / month. Paid plans start at €5.60 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Sample Size API GDPR-compliant?
All requests to Sample Size API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.

Pick an endpoint from the list on the left to see its details and try it.

Code snippets

Sign up to get an API key, then call any path under your slug.

curl https://api.oanor.com/samplesize-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/samplesize-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/samplesize-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);
import requests
r = requests.get(
    "https://api.oanor.com/samplesize-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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