NASA's James Webb Space Telescope

Historical Sensitivity Estimates

This page compares the estimated sensitivities of JWST’s instruments to those of current observatories. The purpose is to help astronomers visualize JWST’s capabilities, and help understand how JWST can advance different science topics. For current best estimates of performance, refer to the JWST Sensitivity and Saturation Limits page which provides values  based on version 1.2 of the JWST Exposure Time Calculator

There are many ways to measure performance: limiting point source flux, limiting line flux; time to survey a given area of the sky or number of spectroscopic targets; and so on. We select illustrative simple cases for 10,000s integrations. For other scenarios, users can scale from the data tables below, or use the ETC. 

The JWST sensitivities reported in the tables and plots below are the mission requirements: the minimum performance required of each instrument. This is a conservative approach and the on-orbit performance may be better. Sensitivities for other observatories are taken from instrument handbooks, online calculators, and published papers, as documented in the data tables.

Photometric Performance

JWST Photometric Performance
Faintest flux for a point source that can be detected at SNR=10 in a 10,000s integration with JWST. Fluxes are given in Jy (left axis) and AB mag (right axis) in both panels, which highlight different wavelength ranges. 


  • The red points are the required sensitivities for JWST's NIRCam (0.6 - 5 micron) and MIRI (5 - 28.3 micron) instruments  
  • The blue points for Hubble are for WFC3, ACS, and (the reddest point) is for NICMOS  
  • Spitzer points are shown in purple (IRAC and MIPS instruments)
  • Gemini points are shown in green (GMOS and NIRI instruments)
  • SOFIA points are shown in cyan (predicted performance for the FLITECAM and FORCAST instruments)
  • Herschel points are shown in black (PACS and SPIRE)
  • ALMA points are shown in grey at two configurations (Cycle 0 array in the top curve and final values in the lower curve)

Spectroscopic Performance for Medium (R=600-3000) and Low (R~100) Resolution

JWST Spectroscopic Performance
Left Panel - Faintest line flux that can be detected at SNR=10 for a point source in a 10,000s integration with JWST.  
Right Panel - Faintest continuum that can be detected at SNR=10 for a point source in 10,000s. Continuum fluxes are in units of Jy (left axis) and AB mag (right axis). 

Legend (Left Panel)

  • The red points show the required performances of JWST's NIRSpec instrument at R=2700 and MIRI in medium resolution mode at R=2400 to 1200, and the expected performance for JWST's NIRCam grisms at R=1000
  • The red curves show the predicted performance of NIRSpec at R=2700 (upper set of curves) and R=1000 (lower set of curves)
  • The black points show IRS on Spitzer, with the SH and LH gratings at R~600
  • Gemini points are shown in green (NIRI at R=1000)
  • Keck points are shown in pink (NIRSPEC at R=1000)
  • VLT points are shown in blue (ISAAC at R=2000 to 3000)
  • SOFIA points are shown in cyan (FLITECAM at R=1700). 

Legend (Right Panel)

  • The red points show the required performance of JWST instruments and the red curves show the expected performance at other wavelengths.
  • The blue points show the performance for the Hubble ACS and WFC3 grisms
  • The black points show the performance of the low-resolution (SL and LL) gratings of IRS/Spitzer at R~60-120