Thermal Conductivity Converter
SI, imperial BTU·in/(hr·ft²·°F) basis per foot thickness as BTU/(hr·ft·°F), and caloric units.
Thermal conductivity, written k, describes how readily a material carries heat: watts crossing a metre of thickness for each kelvin of temperature difference over a square metre of face area. Three unit systems are offered — W/(m·K), BTU/(hr·ft·°F) and cal/(s·cm·°C) — with the SI form held as the internal base, so a larger k typed in produces a proportionally larger figure in every column. The imperial column carries a factor of 1.73073467 W/(m·K); the caloric one carries 418.4, which is why nearly every real material reads as a small fraction there. The trap on this page is per-foot versus per-inch. North American insulation literature usually prints BTU·in/(hr·ft²·°F), a per-inch-of-thickness form, while the unit offered here is per-foot and therefore twelve times smaller for the same material; drop a per-inch figure in untouched and every answer is out by that factor. Nothing here computes R-value or U-factor, both of which fold in a thickness and often air films and framing. It also assumes k is a constant, ignoring its temperature dependence, moisture uptake in porous insulation, and directional variation in fibrous or laminated stock.
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Results
How to Use This Calculator
- Enter k and Unit.
- Review the W/(m·K) result.
- Use BTU/(hr·ft·°F) and cal/(s·cm·°C) to inform your decision.
How the result changes with k
| k | W/(m·K) |
|---|---|
| 0.24 | 0.24 |
| 0.84 | 0.84 |
| 1.56 | 1.56 |
| 2.16 | 2.16 |
What each input means
- k
- Conductivity in selected unit.
- Unit
- BTU unit is per foot of thickness along heat flow.
How this is calculated
Formula
Converted k = Input × (From Factor / To Factor), base unit: W/(m·K)Engine last updated . Checked against 1 independently-derived test — how we verify calculators.
Frequently Asked Questions
Why can I not find my insulation batt's R-value here?
R-value equals thickness divided by conductivity, making it a property of a specific assembly rather than of the substance. This page only restates k between unit systems; you still supply the thickness, and a real wall adds air films and framing on top.
What exactly does the per-foot BTU unit measure?
BTU crossing one square foot of face area each hour, per degree Fahrenheit of difference, across one foot of thickness. The widely published per-inch variant substitutes an inch of thickness, which makes its printed number twelve times larger for identical material.
Why is cal/(s·cm·°C) such an enormous factor?
It stacks two conversions, not three: a calorie is 4.184 joules, and a centimetre is far shorter than a metre, so a rate quoted per centimetre reads 100 times larger once restated per metre. The seconds do not add a third factor — cal/s and W (joules per second) already share the same time base and cancel out. Together those two factors land on 418.4 W/(m·K), so copper and silver land near one in that unit; most other metals sit well below it.
Does k stay constant as a material heats up?
Rarely, and this page assumes it does. Metals typically shed conductivity as they warm, while gases and many insulations gain it, and every published k carries a reference temperature. Convert the figure you have, then check the conditions it was measured under.
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