{
    "name": "Insulation R-Value Calculator",
    "url": "https://calculators.geekmidst.com/calculators/insulation-r-value-calculator",
    "markdown": "https://calculators.geekmidst.com/calculators/insulation-r-value-calculator.md",
    "category": "Construction",
    "description": "Add up the thermal resistance of up to three layers from thickness and conductivity (or R per inch), plus surface films, and get the R-value and U-value.",
    "summary": "Each layer’s R-value is its thickness divided by its thermal conductivity. Layers in series add up, and the U-value is 1 ÷ total R.",
    "also_called": [
        "U-value calculator",
        "Thermal resistance calculator"
    ],
    "applies_to": "Worldwide",
    "last_updated": "2026-10-29",
    "computation": "Results are computed in the visitor’s browser on the HTML page. This API describes the calculator; it does not compute results.",
    "inputs": [
        {
            "name": "units",
            "label": "Units",
            "type": "segmented",
            "default": "metric",
            "options": {
                "metric": "Metric",
                "imperial": "Imperial"
            }
        },
        {
            "name": "t1",
            "label": "Layer 1 thickness",
            "type": "number",
            "default": "100"
        },
        {
            "name": "k1",
            "label": "Layer 1 conductivity or R per inch",
            "type": "number",
            "default": "0.035"
        },
        {
            "name": "t2",
            "label": "Layer 2 thickness",
            "type": "number",
            "default": "12.5",
            "optional": true
        },
        {
            "name": "k2",
            "label": "Layer 2 conductivity or R per inch",
            "type": "number",
            "default": "0.25",
            "optional": true
        },
        {
            "name": "t3",
            "label": "Layer 3 thickness",
            "type": "number",
            "default": "",
            "optional": true
        },
        {
            "name": "k3",
            "label": "Layer 3 conductivity or R per inch",
            "type": "number",
            "default": "",
            "optional": true
        },
        {
            "name": "surface",
            "label": "Surface resistances (inside + outside)",
            "type": "number",
            "default": "0.17",
            "unit": "m²·K/W",
            "optional": true
        }
    ],
    "outputs": [
        {
            "key": "r_si",
            "label": "Total R-value (SI)",
            "format": "number"
        },
        {
            "key": "r_us",
            "label": "Total R-value (US)",
            "format": "number"
        },
        {
            "key": "u_si",
            "label": "U-value",
            "format": "number"
        },
        {
            "key": "u_us",
            "label": "U-factor (US)",
            "format": "decimal4"
        }
    ],
    "formula": {
        "text": "R_layer = t ÷ λ (or t × R per inch);  R_total = Σ R_layer + R_si + R_se;  U = 1 ÷ R_total;  R_US = R_SI × 5.678263",
        "variables": {
            "t": "layer thickness",
            "λ": "thermal conductivity, W/m·K",
            "R_si, R_se": "inside and outside surface resistances"
        }
    },
    "worked_example": {
        "inputs": {
            "units": "metric",
            "t1": "100",
            "k1": "0.035",
            "t2": "12.5",
            "k2": "0.25",
            "t3": "",
            "k3": "",
            "surface": "0.17"
        },
        "steps": [
            "Insulation: 0.100 ÷ 0.035 = 2.857 m²·K/W.",
            "Plasterboard: 0.0125 ÷ 0.25 = 0.050; plus surface films 0.17 → total 3.077 m²·K/W.",
            "U = 1 ÷ 3.077 = 0.325 W/m²·K; US R = 3.077 × 5.678 = R-17.5."
        ],
        "result": "100 mm of 0.035 insulation behind plasterboard gives R 3.08 m²·K/W (about R-17.5 US) and a U-value of 0.325."
    },
    "interpretation": "Higher R (lower U) means less heat flow. Compare the U-value with the target in your energy code, which may count framing and thermal bridges.",
    "assumptions": [
        "Uniform, continuous layers (one-dimensional heat flow)."
    ],
    "limitations": [
        "Studs, fixings and gaps form thermal bridges that lower the real R-value; full calculations (e.g. ISO 6946 combined method) account for them."
    ],
    "rules": null,
    "faqs": [
        {
            "question": "Why are US and metric R-values different numbers?",
            "answer": "They use different units. One SI unit (m²·K/W) equals 5.678 US units (ft²·°F·h/Btu), so R-19 US is about R 3.35 SI."
        },
        {
            "question": "Do air films matter?",
            "answer": "Slightly: about 0.17 m²·K/W on a wall, which matters more for thin, poorly insulated elements such as single glazing."
        }
    ],
    "sources": [],
    "related": [
        {
            "name": "Heat Loss Through Wall Calculator",
            "url": "https://calculators.geekmidst.com/calculators/heat-loss-through-wall-calculator"
        },
        {
            "name": "HVAC Cooling Load Estimate Calculator",
            "url": "https://calculators.geekmidst.com/calculators/hvac-cooling-load-estimate-calculator"
        },
        {
            "name": "Drywall Sheet Count Calculator",
            "url": "https://calculators.geekmidst.com/calculators/drywall-sheet-count-calculator"
        }
    ],
    "disclaimer": "Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials.",
    "publisher": "GM¹X CalcVerse"
}