Enter values with sign convention; leave one blank.
Open the Optics — Lens / Mirror calculator →This is one of 44 tools in the ABC Chemistry Calculator Suite, a free calculator built for IIT-JAM, CSIR-NET, GATE and CUET (Chemical Science) preparation. Nothing is behind a login and no result is stored on a server — the arithmetic runs in your own browser.
The link above opens the suite with Optics — Lens / Mirror already selected, so you do not have to find it in the menu.