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How the ETC WorksScreenshot from ETC.

The new JWST Exposure Time Calculator (ETC) calculates the detailed performance of the observatory by modeling astronomical scenes consisting of single or multiple point and extended sources in three dimensions (two spatial and one wavelength). It offers full support for all of the JWST observing modes, including the NIRSpec and MIRI integral field units, slitless grism spectroscopy with NIRISS and NIRCam and the MIRI and NIRCam coronagraphs. The ETC has a modern web application graphical user interface, which offers advanced functionality for parameter space studies and comparative calculations.



Web Application

The ETC web application represents the official, most up-to-date, version of the JWST ETC. It should be used with JWST Cycle 1 proposals.


JWST ETC web application       User Documentation (JDox)



Python Engine

We also offer the Python engine used by the web ETC. Users who are interested in scripting ETC calculations on their local machine may use this, along with the associated data package. The version numbers of the engine are aligned with those of the web application. Installation and usage instructions can be found on JDox.


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For technical assistance, please contact the JWST Help Desk.


The NASA James Webb Space Telescope, developed in partnership with ESA and CSA, is operated by AURA’s Space Telescope Science Institute.