Convert BTU·inch per Hour-Square Foot-Fahrenheit to Watts per Meter-Kelvin

The BTU·inch per Hour-Square Foot-Fahrenheit (symbol: BTU·in/(hr·ft²·°F)) is a unit of thermal conductivity. An imperial thermal-conductivity unit (≈ 0.1442 W/(m·K) per NIST SP 811 = exactly 1/12 of BTU/(hr·ft·°F)) used almost exclusively for US building-insulation materials. The peculiar 'inch in the numerator' construction lets the unit cancel directly into R-value per unit thickness: an insulation product with k = 0.25 BTU·in/(hr·ft²·°F) achieves R-4 per inch of installed thickness (an R-19 wall = 19/0.25 = ~5 inches of that product). BTU·in/(hr·ft²·°F) is the unit on fiberglass-batt packaging (Owens Corning, Johns Manville, Knauf), rigid-foam-board labels (Dow, Owens Corning Foamular XPS, Dow Thermax polyiso), spray-foam (BASF Walltite, Demilec, Lapolla) data sheets, mineral-wool batts (Rockwool), cellulose loose-fill, and all US Department of Energy ENERGY STAR insulation prescriptive R-value targets. Reference values: fiberglass batt 0.27 BTU·in/(hr·ft²·°F) = R-3.7/in; XPS rigid-foam 0.20 = R-5/in; closed-cell spray foam 0.16 = R-6.5/in; aerogel 0.10 = R-10/in.

It belongs to the imperial measurement system.

BTU·inch per Hour-Square Foot-Fahrenheit are commonly used in insulation design, heat exchanger engineering, and material science.

The Watt per Meter-Kelvin (symbol: W/(m·K)) is a unit of thermal conductivity. The SI unit of thermal conductivity k (ISO 80000-5 §5-9) — the rate of heat flow through a unit thickness of material per unit cross-sectional area per unit temperature gradient, defined by Fourier's law of heat conduction q = −k·∇T. W/(m·K) is the universal reference for steady-state and transient heat-conduction calculations, material selection for thermal management, building-envelope insulation design, and thermal-interface-material specification. Reference values per ASM Handbook and NIST: silver 429 W/(m·K, the highest of common metals); copper 401; aluminum 237; brass 109; carbon steel 50; stainless 304 16; titanium Ti-6Al-4V 6.7; glass 1.0; concrete 1.0-1.7; wood 0.12-0.17 (parallel to grain) / 0.04-0.05 (perpendicular); air at 25 °C 0.026 (this single value is why fiberglass / cellulose / aerogel insulation work — they immobilize air); polystyrene foam (EPS, XPS) 0.030-0.040; fiberglass batt 0.040; aerogel (Aspen Spaceloft) 0.015 — the lowest of common engineering materials. Every CFD solver, thermal-analysis tool (Ansys Mechanical Thermal, COMSOL Heat Transfer, ABAQUS), and building-energy simulation (EnergyPlus, IES VE, DesignBuilder per ASHRAE 90.1 compliance) uses W/(m·K).

It belongs to the metric measurement system.

Watts per Meter-Kelvin are commonly used in insulation design, heat exchanger engineering, and material science.