Heat Transfer Units Conversion Chart
Exact factors between SI and imperial heat transfer units, insulation R-values to RSI and U-values, and the specific heat of water from IAPWS-IF97, with a heat energy calculator.
Heat energy calculator (Q = m × c × ΔT)
2,090 kJ
= 0.5806 kWh = 1,981 BTU · about 11.6 minutes at 3 kW with no losses
Water is about 4.18 kJ/kg·K at room temperature (4.1819 at 25 °C, IAPWS-IF97). 1 BTU/(lb·°F) = 4.1868 kJ/(kg·K).
Standards and method
Every factor is calculated from the exact definitions of the BTU, foot, pound and degree Fahrenheit; specific heat of water is calculated with IAPWS-IF97.
Maintained by Miguel Coelho. Updated . See our editorial policy.
Printable heat transfer units conversion chart
Thermal conductivity, U-value, R-value and RSI, heat transfer coefficient, heat flux and specific heat. Includes the exact definition, formulas, a worked example and sources. Conversion values are checked against the defining constants, and reference data is cited to its source, before the PDF is published.
Free to print, share and use in teaching materials with attribution (CC BY 4.0).
Also in the HVAC and Refrigeration Reference Pack, with related sheets in one PDF.
Full heat transfer units conversion chart
Thermal conductivity, U-value, R-value and RSI, heat transfer coefficient, heat flux and specific heat. These are the same tables as the printable PDF. For: Building services, HVAC and mechanical engineers, energy assessors and students.
- Exact definition
- 1 BTU = 1055.055 852 62 J (IT), 1 ft = 0.3048 m, 1 °F interval = 5/9 K
- Formula
- RSI = R × 0.1761102; U (W/m²·K) = U (IP) × 5.678263
- Reverse
- R = RSI × 5.678263; U-value = 1 ÷ total R-value
- Worked example
- R-19 insulation = 19 × 0.17611 = 3.35 m²·K/W (RSI 3.35), U = 0.299 W/m²·K
- Rounding
- Factors to 7 significant figures; tables to 5. All factors follow from the exact definitions above.
Multiply-by factors
| Quantity | From | To | Multiply by |
|---|---|---|---|
| Thermal conductivity k | BTU/(h·ft·°F) | W/(m·K) | 1.730735 |
| Thermal conductivity k | W/(m·K) | BTU/(h·ft·°F) | 0.5777893 |
| Thermal conductivity k | BTU·in/(h·ft²·°F) | W/(m·K) | 0.1442279 |
| Thermal conductivity k | W/(m·K) | BTU·in/(h·ft²·°F) | 6.933472 |
| Thermal conductivity k | kcal/(h·m·°C) | W/(m·K) | 1.163 |
| U-value, heat transfer coefficient | BTU/(h·ft²·°F) | W/(m²·K) | 5.678263 |
| U-value, heat transfer coefficient | W/(m²·K) | BTU/(h·ft²·°F) | 0.1761102 |
| U-value, heat transfer coefficient | kcal/(h·m²·°C) | W/(m²·K) | 1.163 |
| Thermal resistance R | h·ft²·°F/BTU (R-value) | m²·K/W (RSI) | 0.1761102 |
| Thermal resistance R | m²·K/W (RSI) | h·ft²·°F/BTU (R-value) | 5.678263 |
| Heat flux | BTU/(h·ft²) | W/m² | 3.154591 |
| Heat flux | W/m² | BTU/(h·ft²) | 0.3169983 |
| Specific heat capacity | BTU/(lb·°F) | kJ/(kg·K) | 4.1868 |
| Specific heat capacity | kcal/(kg·°C) | kJ/(kg·K) | 4.1868 |
| Specific heat capacity | kJ/(kg·K) | BTU/(lb·°F) | 0.2388459 |
Insulation R-value to RSI and U-value
| R-value (h·ft²·°F/BTU) | RSI (m²·K/W) | U (W/m²·K) | U (BTU/h·ft²·°F) |
|---|---|---|---|
| 1 | 0.18 | 5.678 | 1.0000 |
| 2 | 0.35 | 2.839 | 0.5000 |
| 3 | 0.53 | 1.893 | 0.3333 |
| 4 | 0.70 | 1.420 | 0.2500 |
| 5 | 0.88 | 1.136 | 0.2000 |
| 6 | 1.06 | 0.946 | 0.1667 |
| 8 | 1.41 | 0.710 | 0.1250 |
| 10 | 1.76 | 0.568 | 0.1000 |
| 11 | 1.94 | 0.516 | 0.0909 |
| 13 | 2.29 | 0.437 | 0.0769 |
| R-value (h·ft²·°F/BTU) | RSI (m²·K/W) | U (W/m²·K) | U (BTU/h·ft²·°F) |
|---|---|---|---|
| 15 | 2.64 | 0.379 | 0.0667 |
| 19 | 3.35 | 0.299 | 0.0526 |
| 21 | 3.70 | 0.270 | 0.0476 |
| 25 | 4.40 | 0.227 | 0.0400 |
| 30 | 5.28 | 0.189 | 0.0333 |
| 38 | 6.69 | 0.149 | 0.0263 |
| 40 | 7.04 | 0.142 | 0.0250 |
| 49 | 8.63 | 0.116 | 0.0204 |
| 50 | 8.81 | 0.114 | 0.0200 |
| 60 | 10.57 | 0.095 | 0.0167 |
U-value (W/m²·K) to imperial U and R-value
| U (W/m²·K) | U (BTU/h·ft²·°F) | R-value (IP) | RSI (m²·K/W) |
|---|---|---|---|
| 0.1 | 0.0176 | 56.8 | 10.00 |
| 0.11 | 0.0194 | 51.6 | 9.09 |
| 0.13 | 0.0229 | 43.7 | 7.69 |
| 0.15 | 0.0264 | 37.9 | 6.67 |
| 0.16 | 0.0282 | 35.5 | 6.25 |
| 0.18 | 0.0317 | 31.5 | 5.56 |
| 0.2 | 0.0352 | 28.4 | 5.00 |
| 0.25 | 0.0440 | 22.7 | 4.00 |
| 0.28 | 0.0493 | 20.3 | 3.57 |
| 0.3 | 0.0528 | 18.9 | 3.33 |
| 0.35 | 0.0616 | 16.2 | 2.86 |
| U (W/m²·K) | U (BTU/h·ft²·°F) | R-value (IP) | RSI (m²·K/W) |
|---|---|---|---|
| 0.45 | 0.0792 | 12.6 | 2.22 |
| 0.5 | 0.0881 | 11.4 | 2.00 |
| 0.7 | 0.1233 | 8.1 | 1.43 |
| 1 | 0.1761 | 5.7 | 1.00 |
| 1.4 | 0.2466 | 4.1 | 0.71 |
| 1.6 | 0.2818 | 3.5 | 0.63 |
| 2 | 0.3522 | 2.8 | 0.50 |
| 2.8 | 0.4931 | 2.0 | 0.36 |
| 4.8 | 0.8453 | 1.2 | 0.21 |
| 5.7 | 1.0038 | 1.0 | 0.18 |
Thermal conductivity
| k (W/m·K) | BTU/(h·ft·°F) | BTU·in/(h·ft²·°F) | kcal/(h·m·°C) |
|---|---|---|---|
| 0.02 | 0.011556 | 0.13867 | 0.017197 |
| 0.025 | 0.014445 | 0.17334 | 0.021496 |
| 0.03 | 0.017334 | 0.208 | 0.025795 |
| 0.035 | 0.020223 | 0.24267 | 0.030095 |
| 0.04 | 0.023112 | 0.27734 | 0.034394 |
| 0.05 | 0.028889 | 0.34667 | 0.042992 |
| 0.1 | 0.057779 | 0.69335 | 0.085985 |
| 0.15 | 0.086668 | 1.04 | 0.12898 |
| 0.2 | 0.11556 | 1.3867 | 0.17197 |
| 0.5 | 0.28889 | 3.4667 | 0.42992 |
| k (W/m·K) | BTU/(h·ft·°F) | BTU·in/(h·ft²·°F) | kcal/(h·m·°C) |
|---|---|---|---|
| 1 | 0.57779 | 6.9335 | 0.85985 |
| 2 | 1.1556 | 13.867 | 1.7197 |
| 5 | 2.8889 | 34.667 | 4.2992 |
| 10 | 5.7779 | 69.335 | 8.5985 |
| 16 | 9.2446 | 110.94 | 13.758 |
| 50 | 28.889 | 346.67 | 42.992 |
| 100 | 57.779 | 693.35 | 85.985 |
| 200 | 115.56 | 1,386.7 | 171.97 |
| 237 | 136.94 | 1,643.2 | 203.78 |
| 401 | 231.69 | 2,780.3 | 344.8 |
Heat transfer coefficient h
| h (W/m²·K) | BTU/(h·ft²·°F) | kcal/(h·m²·°C) |
|---|---|---|
| 2 | 0.35222 | 1.7197 |
| 5 | 0.88055 | 4.2992 |
| 10 | 1.7611 | 8.5985 |
| 25 | 4.4028 | 21.496 |
| 50 | 8.8055 | 42.992 |
| 100 | 17.611 | 85.985 |
| 250 | 44.028 | 214.96 |
| h (W/m²·K) | BTU/(h·ft²·°F) | kcal/(h·m²·°C) |
|---|---|---|
| 500 | 88.055 | 429.92 |
| 1,000 | 176.11 | 859.85 |
| 2,500 | 440.28 | 2,149.6 |
| 5,000 | 880.55 | 4,299.2 |
| 10,000 | 1,761.1 | 8,598.5 |
| 20,000 | 3,522.2 | 17,197 |
| 100,000 | 17,611 | 85,985 |
Typical convection heat transfer coefficients
| Process | h (W/m²·K) | h (BTU/h·ft²·°F) |
|---|---|---|
| Free convection, gases | 2–25 | 0.35–4.4 |
| Free convection, liquids | 50–1,000 | 8.8–176 |
| Forced convection, gases | 25–250 | 4.4–44 |
| Forced convection, liquids | 100–20,000 | 17.6–3,522 |
| Boiling or condensation | 2,500–100,000 | 440–17,611 |
Heat flux
| W/m² | BTU/(h·ft²) | kW/m² |
|---|---|---|
| 1 | 0.317 | 0.001 |
| 10 | 3.17 | 0.01 |
| 50 | 15.85 | 0.05 |
| 100 | 31.7 | 0.1 |
| 500 | 158.5 | 0.5 |
| W/m² | BTU/(h·ft²) | kW/m² |
|---|---|---|
| 1,000 | 317 | 1 |
| 1,361 | 431.43 | 1.361 |
| 5,000 | 1,585 | 5 |
| 10,000 | 3,170 | 10 |
| 100,000 | 31,700 | 100 |
Specific heat of liquid water at 1 atm (IAPWS-IF97)
| T (°C) | T (°F) | cp (kJ/kg·K) | cp (BTU/lb·°F) |
|---|---|---|---|
| 0.01 | 32.02 | 4.2194 | 1.0078 |
| 10 | 50 | 4.1954 | 1.0021 |
| 20 | 68 | 4.1848 | 0.9995 |
| 25 | 77 | 4.1819 | 0.9988 |
| 30 | 86 | 4.1800 | 0.9984 |
| 40 | 104 | 4.1786 | 0.9980 |
| T (°C) | T (°F) | cp (kJ/kg·K) | cp (BTU/lb·°F) |
|---|---|---|---|
| 50 | 122 | 4.1796 | 0.9983 |
| 60 | 140 | 4.1828 | 0.9990 |
| 70 | 158 | 4.1881 | 1.0003 |
| 80 | 176 | 4.1955 | 1.0021 |
| 90 | 194 | 4.2050 | 1.0043 |
| 99 | 210.2 | 4.2154 | 1.0068 |
Heat transfer formulas
| Formula | Meaning | Worked example |
|---|---|---|
| Q = m × c × ΔT | Heat to change the temperature of a mass | Heating 10 kg of water by 50 K: 10 × 4.18 × 50 = 2,090 kJ (0.58 kWh) |
| q = k × A × ΔT ÷ L | Conduction through a slab | k 0.04, 10 m², 20 K, 0.1 m: q = 80 W |
| q = U × A × ΔT | Heat loss through a wall or window | U 0.3, 50 m², 20 K: q = 300 W |
| U = 1 ÷ ΣR | U-value from the layer resistances (including surfaces) | R total 3.33 m²·K/W: U = 0.30 W/m²·K |
| R = L ÷ k | Resistance of one layer | 100 mm at k 0.035: R = 2.86 m²·K/W |
Sources for this chart
Every factor is calculated from the exact definitions of the BTU, foot, pound and degree Fahrenheit; specific heat of water is calculated with IAPWS-IF97.
- NIST Special Publication 811 — Conversion factors; BTU is the International Table BTU (1055.055 852 62 J)
- IAPWS-IF97 (IAPWS R7-97, 2012 revision) — Industrial formulation for the thermodynamic properties of water and steam; reference state u = s = 0 for saturated liquid at the triple point
- Incropera et al., Fundamentals of Heat and Mass Transfer — Table 1.1, typical convection heat transfer coefficients
Related Converters & Charts
Heat Transfer Units Conversion Chart FAQs
Common questions about the heat transfer units conversion chart.
How do you convert R-value to RSI?
Multiply the imperial R-value by 0.17611: R-19 = 3.35 m²·K/W. To go back, multiply RSI by 5.6783.
How do you convert a U-value to an R-value?
R = 1 ÷ U in the same unit system. A U-value of 0.3 W/m²·K is an RSI of 3.33, which is about R-18.9 in imperial units.
How do you convert W/m·K to BTU/(h·ft·°F)?
Multiply by 0.57779. Mineral wool at 0.04 W/m·K is 0.0231 BTU/(h·ft·°F), or 0.277 BTU·in/(h·ft²·°F).
Can I download this chart as a PDF, CSV, or JSON?
Yes. Use the Download A4 PDF or US Letter PDF buttons for a printable version, or download the same tables as CSV or JSON from the links on this page.