Clo Value Calculator - Calculator Academy

Convert between clo and area-based thermal resistance, or sum sourced garment estimates for an indoor outfit. Custom outer layers, headwear and gloves need measured or sourced clo inputs.

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Clo Value Formula

The following formula is used to calculate the Clo value. NIST SP 811 conversion factors support the resistance conversion. Indoor presets and specific garment estimates use ASHRAE Fundamentals, Chapter 9, Tables 7 and 9. The simple garment-sum method follows ASHRAE 55-2010 Addendum h (2013). That historical indoor method excludes clothing above 1.5 clo, highly impermeable clothing and sleeping conditions; no Standard 55 compliance assessment is performed.

Clo = R / 0.155

Variables:

Clo is the Clo value, which represents the thermal insulation provided by clothing.
R is the thermal resistance of the material (m²·K/W).

To calculate the Clo value, divide the thermal resistance of the material by 0.155.

What is a Clo Value?

Clo measures clothing insulation: 1 clo equals 0.155 m²·K/W. It does not guarantee comfort at a particular temperature. Fit, air movement, activity and moisture affect effective insulation. The calculator uses 0.1761102 m²·K/W per ft²·h·°F/Btu (international-table Btu); no inch factor belongs in this area-based resistance unit.

How to Calculate Clo Value?

The following steps outline how to calculate the Clo Value.

First, determine the thermal resistance of the material (R) in m²·K/W.
Next, gather the formula from above: Clo = R / 0.155.
Finally, calculate the Clo Value.
After inserting the variable and calculating the result, check your answer with the calculator above.

Example Problem :

Use the following variable as an example problem to test your knowledge.

Thermal resistance of the material (R) = 0.310 m²·K/W, so clo = 0.310 / 0.155 = 2. This is a unit conversion, not a safe-exposure or comfort rating.