Paint or Stain Coverage Calculator
ANA›Life Services Authority›National Calculator Authority›Paint or Stain Coverage Calculator
.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; } }
Paint or Stain Coverage Calculator
Estimate how many gallons of paint or stain you need for walls, ceilings, fences, or decks — accounting for multiple coats and waste.
Room/Surface Length (ft)
Room/Surface Width (ft) (for floor/ceiling/deck)
Wall Height (ft) (leave 0 for flat surfaces)
Number of Standard Doors (21 sq ft each)
Number of Standard Windows (15 sq ft each)
Number of Coats
1 coat 2 coats 3 coats
Product Coverage Rate (sq ft per gallon)
Waste / Overage Factor (%)
10% — Smooth surface, experienced painter 15% — Typical project 20% — Textured surface or first-time painter 25% — Very rough/porous surface
Calculate
function paiCalc() { var length = parseFloat(document.getElementById('pai-length').value); var width = parseFloat(document.getElementById('pai-width').value); var height = parseFloat(document.getElementById('pai-height').value) || 0; var doors = parseInt(document.getElementById('pai-doors').value) || 0; var windows = parseInt(document.getElementById('pai-windows').value) || 0; var coats = parseInt(document.getElementById('pai-coats').value); var coverage = parseFloat(document.getElementById('pai-coverage').value); var waste = parseFloat(document.getElementById('pai-waste').value);
var resultDiv = document.getElementById('pai-result'); resultDiv.style.display = 'block';
// --- Validation --- if (isNaN(length) || length Please enter a valid Length greater than 0.'; return; } if (isNaN(width) || width Please enter a valid Width greater than 0.'; return; } if (isNaN(coverage) || coverage Please enter a valid Coverage Rate greater than 0.'; return; }
// --- Surface Area Calculation --- var wallArea = 0; var flatArea = 0;
if (height > 0) { // Room walls: perimeter × height // Perimeter = 2 × (length + width) var perimeter = 2 * (length + width); wallArea = perimeter * height; } else { // Flat surface (floor, deck, ceiling, fence panel) flatArea = length * width; }
var totalRawArea = wallArea + flatArea;
// Subtract doors and windows (only meaningful for wall mode) var deductions = (doors * 21) + (windows * 15); if (height Net paintable area is zero or negative. Reduce the number of doors/windows or increase the surface dimensions.'; return; }
// --- Gallons Needed --- // gallons_needed = (net_area × coats) / coverage_rate var gallonsRaw = (netArea * coats) / coverage;
// Apply waste factor // gallons_with_waste = gallons_raw × (1 + waste_factor) var gallonsWithWaste = gallonsRaw * (1 + waste);
// Round up to nearest quart (0.25 gal) for purchase recommendation var gallonsPurchase = Math.ceil(gallonsWithWaste * 4) / 4;
// Whole gallons + quarts breakdown var wholeGallons = Math.floor(gallonsPurchase); var remainingQuarts = Math.round((gallonsPurchase - wholeGallons) * 4);
var purchaseStr = ''; if (wholeGallons > 0 && remainingQuarts > 0) { purchaseStr = wholeGallons + ' gallon' + (wholeGallons !== 1 ? 's' : '') + ' + ' + remainingQuarts + ' quart' + (remainingQuarts !== 1 ? 's' : ''); } else if (wholeGallons > 0) { purchaseStr = wholeGallons + ' gallon' + (wholeGallons !== 1 ? 's' : ''); } else { purchaseStr = remainingQuarts + ' quart' + (remainingQuarts !== 1 ? 's' : ''); }
// Surface type label var surfaceLabel = height > 0 ? 'Wall' : 'Flat Surface';
resultDiv.innerHTML = '### Results ' + '' + '' + surfaceLabel + ' Area (gross)' + totalRawArea.toFixed(1) + ' sq ft' + (height > 0 ? 'Deductions (doors + windows)−' + deductions.toFixed(1) + ' sq ft' : '') + 'Net Paintable Area' + netArea.toFixed(1) + ' sq ft' + 'Coats' + coats + '' + 'Total Area to Cover' + (netArea * coats).toFixed(1) + ' sq ft' + 'Gallons (before waste)' + gallonsRaw.toFixed(2) + ' gal' + 'Waste Factor' + (waste * 100).toFixed(0) + '%' + 'Gallons (with waste)' + gallonsWithWaste.toFixed(2) + ' gal' + 'Recommended Purchase' + gallonsPurchase.toFixed(2) + ' gal (' + purchaseStr + ')' + '' + 'Coverage rate used: ' + coverage + ' sq ft/gal. Always buy a little extra — leftover paint is useful for touch-ups.
'; }
#### Formulas Used
Wall Area (rooms): Wall Area = 2 × (Length + Width) × Height
Flat Surface Area (decks, ceilings, floors): Flat Area = Length × Width
Net Paintable Area: Net Area = Gross Area − (Doors × 21 sq ft) − (Windows × 15 sq ft)
Gallons Required (before waste): Gallons = (Net Area × Number of Coats) ÷ Coverage Rate (sq ft/gal)
Gallons Required (with waste): Gallonsfinal = Gallons × (1 + Waste Factor)
Purchase Quantity: Round up to the nearest quart (0.25 gal) to avoid running short.
#### Assumptions & References
- Standard interior paint coverage is 350–400 sq ft per gallon on smooth surfaces (EPA / paint manufacturer data).
- Exterior paint and stains typically cover 200–300 sq ft per gallon due to surface porosity; adjust the coverage field accordingly.
- A standard door is assumed to be 21 sq ft (3 ft × 7 ft) and a standard window 15 sq ft (3 ft × 5 ft).
- Reference: Painting and Decorating Craftsman's Manual, Painting and Decorating Contractors of America (PDCA).
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