Grease Trap Size Calculator
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.calc-container { max-width: 640px; margin: 2rem 0; padding: 1.5rem; background: #fff; border: 1px solid #ddd; border-radius: 8px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); font-family: system-ui, -apple-system, sans-serif; } .calc-container h3 { font-family: Georgia, serif; font-size: 1.15rem; color: #1a1a1a; margin-bottom: 1rem; padding-bottom: 0.5rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-row { display: flex; align-items: center; gap: 0.75rem; margin-bottom: 0.75rem; flex-wrap: wrap; } .calc-row label { min-width: 160px; font-size: 0.9rem; color: #333; font-weight: 500; } .calc-row input[type="number"], .calc-row select { flex: 1; min-width: 120px; max-width: 200px; padding: 0.5rem 0.6rem; border: 1px solid #ccc; border-radius: 4px; font-size: 0.9rem; font-family: system-ui, sans-serif; color: #1a1a1a; background: #fafaf8; } .calc-row input:focus, .calc-row select:focus { outline: none; border-color: var(--ac, #3d5a80); box-shadow: 0 0 0 2px rgba(26,74,138,0.12); } .calc-row .unit { font-size: 0.82rem; color: #888; min-width: 30px; } .calc-btn { display: inline-block; margin-top: 0.5rem; padding: 0.55rem 1.5rem; background: var(--ac, #3d5a80); color: #fff; border: none; border-radius: 4px; font-size: 0.9rem; font-weight: 600; cursor: pointer; font-family: system-ui, sans-serif; } .calc-btn:hover { opacity: 0.9; } .calc-result { margin-top: 1.25rem; padding: 1rem 1.25rem; background: #f0f6fc; border-left: 3px solid var(--ac, #3d5a80); border-radius: 0 6px 6px 0; display: none; } .calc-result.visible { display: block; } .calc-result-label { font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.06em; color: #666; margin-bottom: 0.25rem; } .calc-result-value { font-size: 1.6rem; font-weight: 700; color: var(--ac, #3d5a80); } .calc-result-detail { font-size: 0.85rem; color: #555; margin-top: 0.5rem; line-height: 1.5; } .calc-note { margin-top: 1rem; font-size: 0.8rem; color: #888; font-style: italic; } .calc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; margin-top: 0.75rem; } .calc-grid-item { padding: 0.6rem 0.8rem; background: #f8f9fa; border-radius: 4px; border: 1px solid #eee; } .calc-grid-item .label { font-size: 0.75rem; color: #888; text-transform: uppercase; letter-spacing: 0.04em; } .calc-grid-item .value { font-size: 1.1rem; font-weight: 600; color: #1a1a1a; } @media (max-width: 720px) { .calc-row { flex-direction: column; align-items: flex-start; gap: 0.3rem; } .calc-row label { min-width: auto; } .calc-row input[type="number"], .calc-row select { max-width: 100%; width: 100%; } .calc-grid { grid-template-columns: 1fr; } } .calc-chart { margin: 1rem 0; text-align: center; } .calc-chart svg { max-width: 100%; height: auto; } .calc-chart-legend { display: flex; flex-wrap: wrap; justify-content: center; gap: 0.6rem 1.2rem; margin-top: 0.6rem; font-size: 0.8rem; color: #555; } .calc-chart-legend span { display: inline-flex; align-items: center; gap: 0.3rem; } .calc-chart-legend i { display: inline-block; width: 10px; height: 10px; border-radius: 2px; font-style: normal; } .calc-related { max-width: 640px; margin: 2rem 0 1rem; padding: 1.25rem 1.5rem; background: #f8f9fa; border: 1px solid #e8e8e8; border-radius: 8px; } .calc-related h3 { font-family: Georgia, serif; font-size: 1rem; color: #1a1a1a; margin: 0 0 0.75rem; padding-bottom: 0.4rem; border-bottom: 2px solid var(--ac, #3d5a80); } .calc-related-list { list-style: none; padding: 0; margin: 0 0 0.75rem; display: grid; grid-template-columns: 1fr 1fr; gap: 0.4rem 1.5rem; } .calc-related-list li a { font-size: 0.88rem; color: var(--ac, #3d5a80); text-decoration: none; } .calc-related-list li a:hover { text-decoration: underline; } .calc-browse-all { margin: 0.5rem 0 0; font-size: 0.9rem; font-weight: 600; } .calc-browse-all a { color: var(--ac, #3d5a80); text-decoration: none; } .calc-browse-all a:hover { text-decoration: underline; } @media (max-width: 720px) { .calc-related-list { grid-template-columns: 1fr; } }
Grease Trap Size Calculator
Determine the minimum grease trap capacity (in gallons) required for your commercial kitchen or food service facility based on drainage flow rate, retention time, and connected fixture units.
Number of Fixture Units (DFU)
Total drainage fixture units connected to the grease trap (sinks, dishwashers, floor drains, etc.)
Flow Rate per Fixture Unit (GPM)
Typical flow rate per fixture unit. Standard value is 2 GPM per DFU (PDI G101).
Retention Time (minutes)
Time wastewater must remain in the trap for grease separation. Typically 24–30 minutes (PDI G101 uses 30 min).
Grease Storage Factor (%)
Percentage of trap volume reserved for accumulated grease. Typically 25% per PDI G101.
Calculate
function greCalc() { var resultDiv = document.getElementById('gre-result'); resultDiv.style.display = 'none'; resultDiv.className = 'calc-result';
var fixtures = parseFloat(document.getElementById('gre-fixtures').value); var flowRate = parseFloat(document.getElementById('gre-flow-rate').value); var retentionTime = parseFloat(document.getElementById('gre-retention-time').value); var storageFactor = parseFloat(document.getElementById('gre-storage-factor').value);
// --- Validation --- var errors = []; if (isNaN(fixtures) || fixtures 500) { errors.push('Fixture units must be between 1 and 500.'); } if (isNaN(flowRate) || flowRate 20) { errors.push('Flow rate per fixture unit must be between 0.1 and 20 GPM.'); } if (isNaN(retentionTime) || retentionTime 120) { errors.push('Retention time must be between 1 and 120 minutes.'); } if (isNaN(storageFactor) || storageFactor 50) { errors.push('Grease storage factor must be between 10% and 50%.'); }
if (errors.length > 0) { resultDiv.className = 'calc-result calc-error'; resultDiv.innerHTML = 'Please fix the following errors:' + errors.map(function(e){ return ''; }).join('') + ''; resultDiv.style.display = 'block'; return; }
// --- Core Formula (PDI G101) --- // Step 1: Total flow rate (GPM) var totalFlowGPM = fixtures * flowRate;
// Step 2: Working volume of trap (gallons) // Working Volume (gal) = Total Flow Rate (GPM) × Retention Time (min) var workingVolume = totalFlowGPM * retentionTime;
// Step 3: Total trap capacity accounting for grease storage // Total Capacity = Working Volume / (1 - Storage Factor / 100) var storageFraction = storageFactor / 100; var totalCapacity = workingVolume / (1 - storageFraction);
// Step 4: Round up to nearest standard grease trap size var standardSizes = [35, 50, 75, 100, 150, 200, 250, 300, 500, 750, 1000, 1250, 1500, 2000, 2500, 3000]; var recommendedSize = null; for (var i = 0; i = totalCapacity) { recommendedSize = standardSizes[i]; break; } } if (recommendedSize === null) { recommendedSize = Math.ceil(totalCapacity / 500) * 500; }
// Step 5: Pumping frequency estimate // Grease traps should be pumped when 25% capacity is reached (EPA guideline) // Assume average grease accumulation rate ~1 gallon per 100 gallons of wastewater processed var greasePumpCapacity = recommendedSize * storageFraction; var dailyWastewater = totalFlowGPM * 60 * 8; // assume 8-hour operating day var greasePumpingDays = (greasePumpCapacity / (dailyWastewater * 0.01)).toFixed(1);
// --- Output --- resultDiv.innerHTML = '### ✓ Grease Trap Sizing Results ' + '' + 'Total Flow Rate' + '' + totalFlowGPM.toFixed(2) + ' GPM' + 'Required Working Volume' + '' + workingVolume.toFixed(1) + ' gallons' + 'Calculated Total Capacity' + '' + totalCapacity.toFixed(1) + ' gallons' + '▶ Recommended Trap Size' + '' + recommendedSize + ' gallons' + 'Grease Storage Volume' + '' + greasePumpCapacity.toFixed(1) + ' gallons (' + storageFactor + '%)' + 'Est. Pumping Frequency' + 'Every ~' + greasePumpingDays + ' days' + '' + 'ⓘ Always verify sizing with local plumbing codes and a licensed engineer. Actual pumping frequency depends on kitchen usage and grease load.
';
resultDiv.style.display = 'block'; }
#### Formula
Based on PDI Standard G101 (Plumbing & Drainage Institute):
- Total Flow Rate (GPM) = Fixture Units (DFU) × Flow Rate per Fixture (GPM)
- Working Volume (gal) = Total Flow Rate (GPM) × Retention Time (min)
- Total Capacity (gal) = Working Volume ÷ (1 − Grease Storage Factor)
- Recommended Size = Next standard commercial trap size ≥ Total Capacity
Example: 4 DFU × 2 GPM = 8 GPM → 8 × 30 min = 240 gal working volume → 240 ÷ 0.75 = 320 gal → Recommend 500-gallon trap.
#### Assumptions & References
- PDI G101: Standard for Hydromechanical Grease Interceptors — the primary sizing standard used in the US.
- Default flow rate of 2 GPM per DFU is per PDI G101 and most local plumbing codes.
- Default retention time of 30 minutes is the PDI G101 standard; some jurisdictions require 24 minutes.
- Default grease storage factor of 25% is per PDI G101; EPA recommends pumping when 25% capacity is reached.
- This calculator covers hydromechanical (passive) grease traps. Large facilities may require gravity grease interceptors sized differently per ASME A112.14.3.
- References: PDI G101, ASME A112.14.3, EPA Grease Management Guidelines, IPC Section 1003.
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