Online SRI calculator

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Online solar reflectance index (SRI) calculator

3 standard wind conditions for SRI calculation
(0-2 m/s)
(2-6 m/s)
(6-10 m/s)
Black surface temperature
Standard black surface: solar reflectance=0.05, emittance=0.90
White surface temperature
Standard white surface: solar reflectance=0.80, emittance=0.90
Sample surface temperature
Your sample surface, with the solar reflectance and emittance input by you below
Solar reflectance index (SRI)
SRI is the sample surface temperate scaled by the standard black and white surface temperatures
Solar reflectance:
The fraction of solar radiation reflected by a surface. 0 (0%) for a perfect black surface and 1 (100%) for a perfect white surface
Solar absorptance:
The fraction of solar radiation absorbed by a surface. Solar absorptance=1 - solar reflectance.
The ability of a surface to exchange thermal radiation with ambient enviroment. The emittance of most surface is between 0.85 and 0.95.
Temperature unit:
The default temperature unit in SRI calculation is Kelvin.

©OTM Solutions Pte Ltd, V1.1.1, 23/06/2020

How to use the SRI calculator?

Simply input your material’s solar reflectance and emittance to the SRI calculator above and get its SRI instantly.

  • Solar reflectance: the range of solar reflectance is 0 – 1, with 0 for perfect black material and 1 for perfect white. If you know your material’s solar reflectance in percentage, simply convert it to decimal (e.g. 56.7% = 0.567).
  • Emittance: it is often called emissivity. The emittance of most materials is between 0.85 and 0.95. If you are not sure, you can simply use the default value 0.90.

The calculator is based on ASTM E1980-11.

What is solar reflectance index (SRI)?

Please refer to the detailed explanation in the SRI testing service page.

Looking for a professional SRI testing lab?

Please visit our SRI testing service page. Our lab is SAC-SINGLAS (ISO 17025) accredited and our customers are from more than 20 countries.

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Comments or feedback?

Please feel free to leave your comments or feedback to this online calculator in the “Leave a Reply” section at the bottom of this page. We will improve this online calculator regularly.

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5 thoughts on “Online SRI calculator

  • 21/11/2021 at 4:20 am


    I love this calculator! Really easy to use and displays the calculations perfectly. Just to be sure, this calculator assume a certain level of solar irradiance and ambient air temperature right? If that is correct, I think it would be great if you would show those values used and even allow inputting custom air temperatures and solar radiation levels into the calculator. This would make the calculator a lot more useful for areas of different latitudes and climates. Thank you!

    • 06/12/2021 at 12:57 pm

      Hi, John,

      ASTM E1980 is followed in this calculator. The following standard conditions are defined in ASTM E1980: Solar flux = 1000 W/m2, ambient air temperature = 310 K, sky temperature = 300 K. I will write a post on the standard conditions and calculation method shortly. The calculator will not be updated to include the non-standard conditions. However, if you would like to perform non-standard calculations, you may use the MS Excel calculator from LBNL: In this calculator, you should be able to use non-standard conditions.

  • 22/09/2022 at 4:33 am

    does this model use 3-year aged SR or initial SR as an input

    • 23/09/2022 at 11:13 am

      Hi, Stefan,

      The SRI calculation model remains the same for both 3-year aged and initial SRI calculations.

      If you input the initial SR, it returns the initial SRI; if you input the 3-year aged SR, it returns the 3-year aged SRI.


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