Is There A Device For Home Use That Can Measure How Low The Bass In My Speakers Is?

If this is just for curiosity sake, a test tone generator is on many websites including audiocheck as listed above.  Also there are phone apps for SPL, so you can verify the drop in dB, probably not super accurate, but good enough for curiosity. 

@mitch4t 

hypoman is the first, and only, contributor to this thread to even mention an essential parameter relevant to almost every other suggestion: that the SPL meter must be properly "weighted." The meter elliotbnewcombjr actually provides a link to will be useless for measuring bass output: it is "A weighted," which does not register anything below 100 Hz. The vast majority of such inexpensive meters available on Amazon or eBay are "A weighted," like the one in that link, which are intended for measuring industrial noise levels, not music. I learned this the hard way: I acquired one of those "A weighted" meters, and was puzzled that the readings I got seemed impossibly low for the subjective loudness they presumably measured. A device that will allow you to switch between "A" and "C" weighting will dramatically reveal the difference. And since the OP is interested specifically in "how low" his speakers will go, none of the suggested meters in this thread will be of any use at all in determining this.

OP wants HZ but gets SPL (“I didn’t order umm”) suggestions as though he were the brain dead one. LOL. 

OP, there are free versions of tone generators, SPL meters and spectrum analyzers available in the Apple App Store or Google Apps. HSU Research has a test tone CD that has the absolute cleanest 16HZ recordings on the planet, should you be interested in the extreme. I’ve gotten one free with every sub. Probably available for sale on the cheap. It has a bunch of other test pieces as well including music and pink/white noises. In the event you’re looking at 20HZ and up, the free stuff will do nicely. 

(Mr. Anderson was here.)

dgluke complains that suggesting SPL meters when the OP had asked for Hz is "braindead." But--duh!--Hz are audible as SPL. And then dgluke suggests the Hsu test tone CD, like everyone who mentioned SPL readings also did (even if not the Hsu CD specifically).

The easy way to "measure" if your speakers go down to 20 Hz, or 16 Hz (if you’ve got a Hsu sub, apparently) is to play such a test CD and LISTEN! If you can’t HEAR your speaker producing the tone, measure the output with an SPL meter. If you’re still skeptical, take the grill cloth off and watch the cone move.