When you measure a fish, do you go by the length you get if you put the tape from its tail, all the way over to its mouth, or do you place the fish on a flat surface and go by the length that you get measuring on a flat surface?

Flat surface, closed mouth, and pinched tail.

Texas state law requirements to measure a fish with mouth closed, flat surface, and tail pinched.

Is this a standard practive used by other states?

Matt

Michigan is the same as Texas. As explained on page 21 of the fishing guide.

"Length Measurement Directions: Measure fish from tip of nose (or lower jaw) to tip of tail in a straight line (DO NOT measure in a curve around body from nose to tail). Measure to closest 1/8th inch. Tail and jaw should be pinched together."

Falcon

Tennessee - flat surface, closed mouth to pinched tail also. I'm pretty sure that this goes for most, if not all, inland lakes, rivers, and reservoirs.

I keep a "Golden Rule" in my boat that also estimates weight, along with a digital scale, a "grabber" scale, and soft cloth tape measure.

If I go out on the bank, I just take a tape measure and dial scale. You can lay the tape on the ground and, with practice, get a good measurement.

Remember to get both length and girth so that you can calculate weight.

If you forget your tape measure, lay the fish on the ground next to your pole...you can measure your pole later and use the photo to determine length.

Virginia- Flat surface, closed mouth, pinched tale lobes.  I am pretty sure, this is the official way to measure freshwater fish.  If you don't close the mouth or pinch the tale lobes, it makes your fish seem a lot bigger though.  For example the fish in my avatar went 26 inches without the mouth closed or tail lobes pinched, only 23.5 when measured properly.  

In New York the mouth may be open or closed and the tail may be spread or compressed, whichever yields the greatest length. So the answer to your question should really be to check your state's regulations.

same with ohio,

I was figuring that you would go with the flat surface. I was wondering because this bass i just caught was 22" on the flat surface, and 24" on the curve of the fish

This is pretty much a standard around the world and follows the IGFA submission rules.

All freshwater Florida Fish and Wildlife Conservation Commission regulations and the "Big Catch" program depend on "total length." The total length is the maximum length of the fish, with the mouth closed and the tail fin pinched together.  The best way to obtain this length is to push the fish's snout up against a vertical surface with the mouth closed and the fish laying along a tape measure, then pinch the tail fin closed and determine the total length.  Do NOT pull a flexible tape measure along the curve of the fish.  The photo to the right shows a bass on a measuring board with the mouth held shut.  Prior to getting a final measurement the caudal (tail) fin will be pinched shut.

TOTAL LENGTH MEASUREMENT

"Girth" is best measured with a fabric ruler, such as tailors use. It can also be determined by drawing a string around the fish at its widest point marking where the string overlaps and then measuring the distance between the overlapping points on a conventional ruler. The measurement should be taken perpendicular to the length of the fish.  This measurement is analogous to measuring the circumference of someone's waist.  Knowing the girth is important when trying to certify a fish for a record, and provides useful information to biologists about the relative condition of a fish.

GIRTH MEASUREMENT