Irrigation Set Time Calculator
About this app
Free irrigation set time calculator. ETc from ETo × Kc, then hours from application rate.
Irrigation Set Time Calculator Irrigation Set Time Calculator How long to run a set from crop ET and application rate. Uses ETo you already have. Not an ETo engine. Reference EToinches or mm for the period. Same depth unit as the application rate × hours. Crop coefficient Kcdimensionless Net application rateinches/hour or mm/hour, same depth unit as ETo Distribution uniformity DUdecimal. 0.80 = 80%. Optional. Hours_adj = hours / DU. Calculate set time Formula ETc = ETo × Kc hours = ETc / application rate hours with DU = hours / DU Example: ETo = 0.25 in, Kc = 1.1, rate = 0.2 in/h ETc = 0.275 in hours = 1.38 h with DU 0.80 → 1.72 h Kc values are crop and growth-stage specific (FAO-56 Table 12). References Allen RG, et al. FAO Irrigation and Drainage Paper 56. ETc = ETo × Kc. Chapter 6 crop coefficients. USDA NRCS. Irrigation Guide. Set time from net depth and application rate; DU adjustment. Field planning aid only. Confirm rates with your agronomist, label, and local extension. Not a pesticide or fertilizer recommendation.
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Source
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
<title>Irrigation Set Time Calculator</title>
<meta name="description" content="Free irrigation set time calculator. ETc from ETo × Kc, then hours from application rate.">
<meta name="keywords" content="irrigation set time, ETc, crop coefficient, Kc, application rate, sprinkler hours, agronomy">
<style>
:root { --text:#1a1a1a; --muted:#4a4a4a; --line:#d6d6d6; --bg:#fff; --panel:#f6f6f6; }
html { -webkit-text-size-adjust:100%; text-size-adjust:100%; }
* { box-sizing:border-box; }
body {
margin:0;
font:16px/1.45 system-ui,-apple-system,sans-serif;
color:var(--text);
background:var(--bg);
overflow-x:hidden;
}
main {
max-width:720px;
margin:0 auto;
padding:24px 16px 48px;
padding-left:max(16px, env(safe-area-inset-left));
padding-right:max(16px, env(safe-area-inset-right));
}
html.in-viewer main {
padding-top:calc(4.25rem + env(safe-area-inset-top, 0px));
padding-right:calc(4.75rem + env(safe-area-inset-right, 0px));
padding-bottom:calc(6.5rem + env(safe-area-inset-bottom, 0px));
}
h1 { font-size:1.35rem; margin:0 0 0.35rem; }
h2 { font-size:1.05rem; margin:1.75rem 0 0.5rem; }
p, li { color:var(--text); }
.lede, .note, .disclaimer, label span { color:var(--muted); }
.lede, .disclaimer { font-size:0.95rem; }
label span { font-weight:400; font-size:0.85rem; }
form, .stack { display:grid; gap:14px; margin:1.25rem 0; }
fieldset {
border:1px solid var(--line);
border-radius:6px;
padding:12px;
display:grid;
gap:12px;
min-width:0;
}
legend { font-weight:600; padding:0 6px; }
label { display:grid; gap:4px; font-weight:600; }
.check { display:flex; align-items:center; gap:10px; font-weight:600; }
.check input { width:22px; height:22px; min-height:22px; flex:0 0 auto; }
input, select, textarea {
font:inherit;
font-size:16px;
min-height:44px;
padding:10px 12px;
border:1px solid var(--line);
border-radius:6px;
width:100%;
max-width:100%;
background:#fff;
}
button {
font:inherit;
font-size:16px;
font-weight:600;
width:100%;
min-height:48px;
padding:12px 14px;
border:0;
border-radius:6px;
background:#1a1a1a;
color:#fff;
cursor:pointer;
}
.result {
padding:16px;
background:var(--panel);
border:1px solid var(--line);
border-radius:6px;
}
.result strong { font-size:1.35rem; }
.parts { display:grid; gap:6px; margin-top:10px; font-size:0.95rem; }
pre.formula {
white-space:pre-wrap;
overflow-wrap:anywhere;
background:var(--panel);
border:1px solid var(--line);
border-radius:6px;
padding:12px;
font-size:0.9rem;
max-width:100%;
}
ol.refs { padding-left:1.25rem; }
ol.refs li { margin-bottom:0.6rem; }
a { color:inherit; }
.table-wrap { overflow-x:auto; -webkit-overflow-scrolling:touch; max-width:100%; }
table { border-collapse:collapse; width:100%; font-size:0.9rem; }
th, td { border:1px solid var(--line); padding:8px; text-align:left; vertical-align:top; }
.muted { color:var(--muted); font-size:0.9rem; }
</style>
</head>
<body>
<main>
<h1>Irrigation Set Time Calculator</h1>
<p class="lede">How long to run a set from crop ET and application rate. Uses ETo you already have. Not an ETo engine.</p>
<form id="calc-form">
<label>Reference ETo<span>inches or mm for the period. Same depth unit as the application rate × hours.</span>
<input id="eto" type="number" min="0" step="any" inputmode="decimal" value="0.25">
</label>
<label>Crop coefficient Kc<span>dimensionless</span>
<input id="kc" type="number" min="0" step="any" inputmode="decimal" value="1.1">
</label>
<label>Net application rate<span>inches/hour or mm/hour, same depth unit as ETo</span>
<input id="rate" type="number" min="0" step="any" inputmode="decimal" value="0.2">
</label>
<label>Distribution uniformity DU<span>decimal. 0.80 = 80%. Optional. Hours_adj = hours / DU.</span>
<input id="du" type="number" min="0" max="1" step="any" inputmode="decimal" value="0.8">
</label>
<button type="submit">Calculate set time</button>
</form>
<div class="result" id="result" hidden></div>
<h2>Formula</h2>
<pre class="formula">ETc = ETo × Kc
hours = ETc / application rate
hours with DU = hours / DU
Example: ETo = 0.25 in, Kc = 1.1, rate = 0.2 in/h
ETc = 0.275 in
hours = 1.38 h
with DU 0.80 → 1.72 h
Kc values are crop and growth-stage specific (FAO-56 Table 12).</pre>
<h2>References</h2>
<ol class="refs">
<li>Allen RG, et al. FAO Irrigation and Drainage Paper 56. ETc = ETo × Kc. Chapter 6 crop coefficients.</li>
<li>USDA NRCS. Irrigation Guide. Set time from net depth and application rate; DU adjustment.</li>
</ol>
<p class="disclaimer">Field planning aid only. Confirm rates with your agronomist, label, and local extension. Not a pesticide or fertilizer recommendation.</p>
</main>
<script>
if (window.self !== window.top) {
document.documentElement.classList.add('in-viewer');
}
function num(id) {
var el = document.getElementById(id);
if (!el) return 0;
var value = parseFloat(el.value);
return isFinite(value) && value > 0 ? value : 0;
}
function raw(id) {
var el = document.getElementById(id);
if (!el) return NaN;
var value = parseFloat(el.value);
return isFinite(value) ? value : NaN;
}
function sel(id) {
var el = document.getElementById(id);
return el ? el.value : '';
}
function showResult(html) {
var el = document.getElementById('result');
el.hidden = false;
el.innerHTML = html;
}
function fmt(value, digits) {
if (!isFinite(value)) return '—';
return value.toFixed(digits);
}
document.getElementById('calc-form').addEventListener('submit', function (event) {
event.preventDefault();
var eto = num('eto'), kc = num('kc'), rate = num('rate'), du = raw('du');
if (!eto || !kc || !rate) {
showResult('<p>Enter ETo, Kc, and application rate greater than zero.</p>');
return;
}
var etc = eto * kc;
var hours = etc / rate;
var adj = isFinite(du) && du > 0 && du <= 1 ? hours / du : hours;
showResult(
'<div>Set time</div><strong>' + fmt(hours, 2) + '</strong><span> hours (net)</span>' +
'<div class="parts"><div>ETc = ' + fmt(etc, 3) + ' depth units</div>' +
(isFinite(du) && du > 0 ? '<div>With DU ' + fmt(du, 2) + ' = ' + fmt(adj, 2) + ' hours</div>' : '') +
'</div>'
);
});
</script>
</body>
</html>
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