Heat Transfer Coefficient Converter: U-Value & 11 Units
Convert U-value and heat transfer coefficient between W/(m²·K), Btu/(ft²·h·°F), and 11 units—building envelopes, heat exchangers, and convection.
Convert heat transfer coefficient (U-value, h) between W/(m²·K), Btu/(ft²·h·°F), kcal/(m²·h·°C), and 11 units. Essential for building envelopes, heat exchangers, and convection. Free, runs in your browser—no sign-up.
What is the heat transfer coefficient?
The heat transfer coefficient (U or h) is heat flow per unit area per unit temperature difference—how many watts pass through each square meter for each kelvin (or degree) of ΔT. SI unit is W/(m²·K). In building science it’s called U-value; in the US you often see Btu/(h·ft²·°F). It links heat flux to temperature drop:
So for a given U (W/(m²·K)), area A (m²), and ΔT (K), you get total heat flow q in watts. U is the inverse of thermal resistance per area: U = 1/(R·A) for a layer, so low U means better insulation. This converter handles all 11 supported units so you can match specs from different regions and disciplines.
Key units explained
W/(m²·K)
Factor: 1 (SI base)
Standard U-value. Typical wall 0.2–0.5; single pane ~6; double pane ~3.
Btu/(ft²·h·°F)
Factor: 1 ≈ 5.678 W/(m²·K)
US building and HVAC. R-value in °F·ft²·h/Btu is 1/U in this unit.
kcal/(m²·h·°C)
Factor: 1 ≈ 1.163 W/(m²·K)
Metric thermal conductance per area. Common in older European literature.
CHU/(ft²·h·°C)
Factor: 1 CHU = 0.5 Btu
Celsius heat unit per area per °C. Converts like Btu/(ft²·h·°F) with °C.
Who uses this converter?
Building and HVAC engineers switch between W/(m²·K) and Btu/(ft²·h·°F) for envelope and code compliance. Window and insulation specs often mix SI and US units. Heat exchanger design uses U for overall conductance. Students need consistent units for q = U·A·ΔT and for relating U to R-value. All 11 units are in one tool; conversions run locally.
Common conversions at a glance
| From | To | Formula |
|---|---|---|
| W/(m²·K) | Btu/(ft²·h·°F) | ÷ 5.678 |
| Btu/(ft²·h·°F) | W/(m²·K) | × 5.678 |
| W/(m²·K) | kcal/(m²·h·°C) | × 0.8598 |
Avoiding common mistakes
Don’t confuse U-value (conductance per area, W/(m²·K)) with R-value (resistance, m²·K/W or °F·ft²·h/Btu). U = 1/R for a single layer of area A when R is total thermal resistance. Use our Thermal Resistance converter for R. Keep temperature units consistent: °F with Btu/(ft²·h·°F), K or °C with W/(m²·K)—numerically 1 K = 1 °C for ΔT. Check whether the source means overall U (whole assembly) or surface film coefficient (h).
Heat Transfer Coefficient FAQ
? How do I convert U-value from Btu/(ft²·h·°F) to W/(m²·K)?
Multiply by about 5.678. So 1 Btu/(ft²·h·°F) ≈ 5.678 W/(m²·K). Use the converter above for exact values and for kcal/(m²·h·°C), CHU/(ft²·h·°C), and the other supported units.
? What is the relationship between U-value and R-value?
For a single layer or assembly, U = 1/R when R is thermal resistance per unit area (m²·K/W). So R = 5 m²·K/W gives U = 0.2 W/(m²·K). In US units, R in °F·ft²·h/Btu and U in Btu/(ft²·h·°F) also satisfy U = 1/R. Use our Thermal Resistance converter to switch R between SI and US.
? When do I use U vs h for heat transfer coefficient?
U usually means overall coefficient for a composite (wall, window, heat exchanger). h often means surface or film coefficient (convection only). Same units—W/(m²·K)—so this converter works for both. Building codes and labels typically report U-value.
? What is a good U-value for a wall or window?
Well-insulated walls are often 0.2–0.3 W/(m²·K); passive house targets can be lower. Single-pane windows are around 5–6; double pane about 2.5–3; triple pane or low-E can be under 1. Lower U means less heat loss. Use this converter to switch between W/(m²·K) and Btu/(ft²·h·°F) for code or spec sheets.
? How do I convert kcal/(m²·h·°C) to W/(m²·K)?
Multiply by about 1.163. So 1 kcal/(m²·h·°C) ≈ 1.163 W/(m²·K). The converter above handles kcal/(m²·h·°C), CHU/(ft²·h·°C), and all 11 supported units so you can match European or older metric literature.
? What does U-value mean for windows and insulation?
U-value (or U-factor) is the heat transfer coefficient of the whole assembly—how many watts pass per square meter per kelvin of temperature difference. Lower U means better insulation. Window labels in the US often show U in Btu/(ft²·h·°F); EU and physics use W/(m²·K). This converter covers both and 9 other units.