Quick background first. Voice frequency is how many times your vocal folds vibrate each second while you talk. A lower number means a deeper voice. Most men speak somewhere near 100 to 130 Hz on an average day and most women closer to 190 to 230 Hz, though honestly there's a lot of overlap and a lot of variety. Your number is just your number.

Doing the test

Open Pitchtest.com. It works on a laptop or phone, no app needed. Click allow when your browser asks about the microphone. Skip that and the pitch detector just sits there doing nothing, which confuses more people than you'd think.

Now talk. Normally. Don't put on a "test voice" because everyone does this and it throws the result off. Read a paragraph out loud, describe your morning, count slowly to twenty, whatever. You'll see the numbers move around quite a bit while you speak, and that's fine. Speech naturally rises and falls. What you're after is where it keeps coming back to.

Watch for thirty seconds or so and note the range it hovers in. The middle of that range is your average speaking frequency. Some people also like to hum one comfortable, steady note, since a held tone gives a cleaner single reading.

Getting numbers you can trust

A few things mess with accuracy. Background hum from an AC or fridge, sitting too far from the mic, whispering. A cold or a late night will pull your voice lower too, so if a reading looks odd, try again another day. Two or three sessions averaged together beats one.

Why bother at all? Plenty of reasons. Speakers and presenters want to know if nerves push their voice up. Podcasters like to stay consistent between episodes. People doing voice training track small changes over weeks, and a pitch detector shows those shifts long before your ears notice them. Some folks are just curious, which is a perfectly good reason too.
So give it a go. Open https://pitch-detector.org/, say a few sentences and let the pitch detector give you your number. Takes less time than making tea.