Heat converters
Heat Transfer Coefficient Converter
Convert W/(m²·K), BTU/(h·ft²·°F), kcal/(h·m²·°C) and related U-value units.
Result
0.17611 BTU/(h·ft²·°F)
1 W/(m²·K) = 0.17611 BTU/(h·ft²·°F)
All units for this value
| Unit | Symbol | Value |
|---|---|---|
| Watt per m² per kelvin | W/(m²·K) | 1 |
| Watt per m² per °C | W/(m²·°C) | 1 |
| Kilowatt per m² per kelvin | kW/(m²·K) | 0.001 |
| Watt per cm² per °C | W/(cm²·°C) | 0.0001 |
| Kilocalorie (IT) per hour per m² per °C | kcal/(h·m²·°C) | 0.859845 |
| Calorie (IT) per second per cm² per °C | cal/(s·cm²·°C) | 0.0000238846 |
| BTU (IT) per hour per ft² per °F | BTU/(h·ft²·°F) | 0.17611 |
| BTU (IT) per second per ft² per °F | BTU/(s·ft²·°F) | 0.0000489195 |
About this calculator
The heat transfer coefficient, often called a U-value, describes how much heat passes through a surface per unit area for each degree of temperature difference across it, a key figure in building insulation and equipment design. This converter switches between the SI unit W/(m²·K) and the BTU/(h·ft²·°F) unit widely used in US building codes.
How it works in plain English
A heat transfer coefficient combines a power unit, an area unit, and a temperature-interval unit into one compound measurement, so the converter anchors every value to watts per square meter per kelvin. Because a kelvin and a Celsius degree represent the same size step, W/(m²·K) and W/(m²·°C) are identical numbers, letting the converter treat them as the same unit.
The BTU-based unit divides the International Table BTU (1055.05585262 joules) by an hour (3600 seconds), a square foot (0.09290304 m²), and a Fahrenheit degree (five-ninths of a kelvin), combining to a factor of about 5.678263 W/(m²·K) per BTU/(h·ft²·°F). This is why US-published window and wall U-values, which are often small numbers like 0.3, correspond to noticeably different-looking metric U-values.
Enter a value with your chosen from and to units, and the result updates immediately, backed by a full table of the same coefficient expressed in every supported unit. A precision control sets how many decimal places display, and a swap button reverses the two selected units in one click.
The formula
- value_in_target = value_in_source × (source factor to W/(m²·K)) ÷ (target factor to W/(m²·K))
- 1 BTU(IT)/(h·ft²·°F) = 1055.05585262 ÷ 3600 ÷ 0.09290304 ÷ (5/9) = 5.678263 W/(m²·K)
- 1 kcal(IT)/(h·m²·°C) = 4186.8 ÷ 3600 = 1.163 W/(m²·K)
- 1 W/(m²·°C) = 1 W/(m²·K)
Worked example
Suppose a US window specification lists a U-value of 0.30 BTU/(h·ft²·°F), typical of a good double-glazed unit, and an architect wants that expressed in the metric W/(m²·K) form used on a European energy-efficiency label. Multiplying by the conversion factor: 0.30 × 5.678263 = 1.7035 W/(m²·K).
Entering 0.30 into the BTU/(h·ft²·°F) field with W/(m²·K) selected as the target returns about 1.7035 W/(m²·K) immediately. As a sanity check, that result falls within the roughly 1.4-2.8 W/(m²·K) range typically quoted for double-glazed windows, so it lines up with what's expected for that type of glazing rather than looking like an outlier. The full unit table also shows this same U-value equals roughly 1.4645 kcal/(h·m²·°C), confirming the window performs similarly whichever labeling standard is used to describe it.
Heat transfer coefficient (U-value) reference values
| Quantity | Value in W/(m²·K) |
|---|---|
| 1 BTU(IT)/(h·ft²·°F) | 5.678263 |
| 1 kcal(IT)/(h·m²·°C) | 1.163 |
| Single-pane window (typical) | ≈5.7-6.0 |
| Double-glazed window (typical) | ≈1.4-2.8 |
| Well-insulated wall (typical) | ≈0.2-0.4 |
Standard unit definitions and typical building component ranges
Frequently asked questions
What does a lower U-value mean for a building material?
A lower U-value means less heat passes through the material for a given temperature difference, so the material insulates better. This is the opposite of R-value, where a higher number means better insulation; U-value and R-value are reciprocals of each other once matching units are used.
Why is 1 BTU/(h·ft²·°F) worth about 5.68 W/(m²·K)?
That factor is the product of four separate conversions applied together: the BTU-to-joule factor, the hour-to-second factor, the square-foot-to-square-meter factor, and the Fahrenheit-degree-to-kelvin factor. Multiplying the BTU and dividing by the other three gives the combined figure of approximately 5.678263 used throughout this converter.
Are W/(m²·K) and W/(m²·°C) really the same unit?
Yes. A one-kelvin temperature difference and a one-degree-Celsius temperature difference are exactly the same size, differing only in where their zero points sit. Since a heat transfer coefficient depends on the size of the temperature difference rather than an absolute temperature, both notations give identical numeric results.
How does a U-value relate to thermal resistance or R-value?
A U-value is the mathematical reciprocal of the total thermal resistance across a surface, once consistent units are used, so a material with double the R-value has half the U-value. This converter focuses on U-value units directly; a separate thermal resistance converter handles R-value-style units.
Can I compare a US window rating directly against a European one?
Yes, once both are converted into the same unit. Enter the US BTU/(h·ft²·°F) figure, select W/(m²·K) as the target, and compare the result against the European label's stated value. Because both describe the same physical property, a correct conversion makes the two ratings directly comparable.
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