https://www.stsci.edu/hst/instrumentation/wfc3/software-tools/exposure-time-calculators
Exposure Time Calculators | STScI
The WFC3 Exposure Time Calculators (ETCs) are online tools that predict the count rates and S/N in various observing modes given specified source...
exposure time calculators
https://hst-docs.stsci.edu/cosihb/chapter-7-exposure-time-calculator-etc/7-1-the-cos-exposure-time-calculators
7.1 The COS Exposure Time Calculators - HST User Documentation
exposure time calculatorscoshstuserdocumentation