Conversions Energy and Heat (2024 Guide) | CalcDomain

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          <h1 class="text-3xl font-bold mb-4">Energy &amp; Heat Conversions</h1>
          <p class="text-gray-700 mb-5">
            Convert between the most common energy and heat units: joule (J), kilojoule (kJ), calorie (cal), kilocalorie (kcal), BTU (IT), watt-hour (Wh), kilowatt-hour (kWh), and therm (US). Ideal for engineering, HVAC, physics homework, cooking and energy reports.
          </p>

          <div id="error-box" class="error-box mb-4 hidden">
            <p id="error-msg" class="text-sm">Please enter a numeric energy value.</p>
          </div>

          <div class="grid grid-cols-1 md:grid-cols-3 gap-4 items-end mb-6">
            <div>
              <label for="energy-value" class="block mb-1 font-semibold">Value</label>
              <input id="energy-value" type="number" step="any" value="1000" class="w-full border border-gray-300 rounded-md px-3 py-2" />
            </div>
            <div>
              <label for="energy-from" class="block mb-1 font-semibold">From</label>
              <select id="energy-from" class="w-full border border-gray-300 rounded-md px-3 py-2"></select>
            </div>
            <div>
              <label for="energy-to" class="block mb-1 font-semibold">To</label>
              <select id="energy-to" class="w-full border border-gray-300 rounded-md px-3 py-2"></select>
            </div>
          </div>

          <div class="flex gap-3 items-center mb-4">
            <button id="convert-btn" class="bg-blue-600 hover:bg-blue-700 text-white font-semibold py-2 px-4 rounded-md" type="button">Convert</button>
            <button id="swap-btn" class="bg-gray-100 hover:bg-gray-200 text-gray-800 font-semibold py-2 px-4 rounded-md" type="button">Swap</button>
            <p id="last-conv" class="text-sm text-gray-600">1000 J → 1.0000 kJ</p>
          </div>

          <div class="mb-6 bg-gray-50 border border-gray-200 rounded-md p-4 flex items-center justify-between gap-4">
            <div>
              <p class="text-xs uppercase tracking-wide text-gray-500 mb-1">Result</p>
              <p id="energy-result" class="text-2xl font-bold">1.0000</p>
            </div>
            <button id="copy-btn" class="bg-white border border-gray-200 rounded-md text-sm text-gray-700 hover:bg-gray-100 px-3 py-1" type="button">Copy</button>
          </div>

          <h2 class="text-xl font-semibold mb-3">Reference table</h2>
          <div class="scroll-x mb-6">
            <table>
              <thead>
                <tr>
                  <th>Unit</th>
                  <th>Symbol</th>
                  <th>To joule (J)</th>
                  <th>Notes</th>
                </tr>
              </thead>
              <tbody>
                <tr><td>Joule</td><td>J</td><td>1</td><td>SI base unit</td></tr>
                <tr><td>Kilojoule</td><td>kJ</td><td>1000</td><td>1 kJ = 1000 J</td></tr>
                <tr><td>Calorie (small)</td><td>cal</td><td>4.184</td><td>Thermochemical</td></tr>
                <tr><td>Kilocalorie</td><td>kcal</td><td>4184</td><td>Food “Calorie”</td></tr>
                <tr><td>BTU (IT)</td><td>BTU</td><td>1055.05585262</td><td>HVAC, heating</td></tr>
                <tr><td>Watt-hour</td><td>Wh</td><td>3600</td><td>Power × time</td></tr>
                <tr><td>Kilowatt-hour</td><td>kWh</td><td>3,600,000</td><td>Utility bills</td></tr>
                <tr><td>Therm (US)</td><td>thm</td><td>105,480,400</td><td>Natural gas billing</td></tr>
              </tbody>
            </table>
          </div>

          <div class="prose">
            <h2>Formulas</h2>
            <div class="formula-box">
              <p><strong>General method</strong>: first convert to joules, then from joules to the target unit.</p>
              <p>\( \text{J} = \text{value} \times \text{factor\_to\_joule(from)} \)</p>
              <p>\( \text{target} = \text{J} \div \text{factor\_to\_joule(to)} \)</p>
            </div>
            <h3>Examples</h3>
            <p><strong>1)</strong> Convert 2 kWh to kJ:</p>
            <p>2 kWh × 3,600,000 J/kWh = 7,200,000 J → ÷1000 = 7200 kJ</p>
            <p><strong>2)</strong> Convert 500 cal to BTU:</p>
            <p>500 × 4.184 = 2092 J → 2092 ÷ 1055.05585262 ≈ 1.983 BTU</p>

            <h3>Energy vs heat</h3>
            <p>In thermodynamics, heat is energy in transit due to temperature difference. Here we treat them both as energy quantities and let you jump between common engineering and cooking units.</p>
          </div>

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            (function(){
              const valueEl = document.getElementById('energy-value');
              const fromEl = document.getElementById('energy-from');
              const toEl = document.getElementById('energy-to');
              const resEl = document.getElementById('energy-result');
              const lastEl = document.getElementById('last-conv');
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              const errMsg = document.getElementById('error-msg');
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              // factors: unit -> joules
              const units = {
                "joule (J)": 1,
                "kilojoule (kJ)": 1000,
                "calorie (cal)": 4.184,
                "kilocalorie (kcal)": 4184,
                "BTU (IT)": 1055.05585262,
                "watt-hour (Wh)": 3600,
                "kilowatt-hour (kWh)": 3600000,
                "therm (US)": 105480400
              };

              function fillSelect(sel){
                sel.innerHTML = "";
                Object.keys(units).forEach(u => {
                  const opt = document.createElement('option');
                  opt.value = u;
                  opt.textContent = u;
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              }

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              fillSelect(fromEl);
              fillSelect(toEl);

              fromEl.value = "joule (J)";
              toEl.value = "kilojoule (kJ)";

              function doConvert(){
                clearError();
                const v = parseFloat(valueEl.value);
                if (isNaN(v)){
                  showError("Please enter a numeric energy value.");
                  return;
                }
                const from = fromEl.value;
                const to = toEl.value;
                const j = v * units[from];
                const out = j / units[to];
                resEl.textContent = out.toFixed(6);
                lastEl.textContent = `${v} ${from} → ${out.toFixed(6)} ${to}`;
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              valueEl.addEventListener('input', doConvert);
              fromEl.addEventListener('change', doConvert);
              toEl.addEventListener('change', doConvert);

              // init
              doConvert();
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          </script>
        </div>



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                  <li>
                    <a href="https://www.nist.gov/pml/owm/metric-si/si-units" class="text-blue-600 hover:underline" target="_blank" rel="noopener">
                      NIST: The International System of Units (SI)
                    </a>
                  </li>
                  <li>
                    <a href="https://openstax.org/details/books/college-algebra" class="text-blue-600 hover:underline" target="_blank" rel="noopener">
                      OpenStax: College Algebra
                    </a>
                  </li>
                </ul>
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<section class="bg-white p-4 rounded-lg shadow-md mt-6"><h2 class="text-lg font-semibold mb-2">Inputs used by this calculator</h2><ul class="text-sm text-gray-700 list-disc pl-5"><li>Value</li><li>From</li><li>To</li></ul></section><section class="bg-white p-4 rounded-lg shadow-md mt-6"><h2 class="text-lg font-semibold mb-2">Consistency checks</h2><p class="text-sm text-gray-700">Checks: non-negative values, plausible ranges, coherent outputs.</p></section><section class="bg-white p-4 rounded-lg shadow-md mt-6"><h2 class="text-lg font-semibold mb-2">Operational notes</h2><p class="text-sm text-gray-700">Fill in realistic values and keep units and timeframes consistent.</p><p class="text-sm text-gray-700 mt-2">Key entities: Conversions, Energy, And, Heat, Value, From, To.</p></section><section class="bg-white p-4 rounded-lg shadow-md mt-6"><h2 class="text-lg font-semibold mb-2">Inputs used by this calculator</h2><ul class="text-sm text-gray-700 list-disc pl-5"><li>Value</li><li>From</li><li>To</li></ul></section><section class="bg-white p-4 rounded-lg shadow-md mt-6"><h2 class="text-lg font-semibold mb-2">Consistency checks</h2><p class="text-sm text-gray-700">Checks: non-negative values, plausible ranges, coherent outputs.</p></section><!-- %%EEAT_STRIP%% -->
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