What temperature of thermostat do you have?  That has something to do with what your gauge reads.  Gauges read differently from car to car, so we can't tell you what yours says although, a reading in the middle of the gauge usually means the water is the temp of your thermostat.  

You might take your reading from the water in the radiator.  Remove the cap when the car is up to temp and just after turning off the car to insure internal pressure doesn't come up to burn you.

I recently had a 160deg thermostat in my car and the temp gauge only read maybe a 1/4 (if that). After seeing some discussion on here about thermostats, I took Mustang Steve's advice and fitted a 191deg thermostat. Currently, my temp gauge is reading a solid 1/2 and this was at night. I am wondering if I may have gone too hot.

Those numberless gages are a guess. Lower 1/3 is too cold. Middle 1/3 somewhere is just right, top 1/3 is too hot.  I believe Ford intended the half way mark for decades to be “just right,” whatever that is.  On my ‘92 5.0 that stock gage read dead middle for over 20 years.  No matter how cold or hot it was outside dead middle was where it always sat. The bottom mark is 130 and the top mark is 270 so I figured the middle mark was 200. That gage has become nearly useless. I measure its uselessness by a new AutoMeter pillar mounted gage I installed which seems to function rationally. The old stock gage with a new sender registers 10-30 degrees hotter than the AutoMeter at any given time. My engine is at 27 years old and 292K miles and with cooling system upgrades AutoMeter says I never reach 210 even in 105+ heat, A/C full blast, idling at In-n-Out. Stock gage wants me to believe its 240.

rtmjr13@optonline.net wrote:

Hello all, 67 mustang 390 gt.
Was wondering what temp would the motor be at if the gauge was reading in the middle. On a hot day like today mine is reading way low, I put a infer red thermometer on different parts of the motor, hottest spots only read about 150 deg. Give or take a few. Edelbrock Aluminum heads and intake, 4 core 23 in radiator, 7 blade 18.25 fan and shroud . What temp would the gauge be reading at dead center?

Hi , times ago i post the result of reading with a digital sender and what the old gauge means on  the rise . 
I think was " true temp reading " 
check it 

When you use an infrared temp gun, I would suggest the following. 
Place a piece if black electric tape on the surface you’re checking.
Otherwise your temperature readings will be inaccurate. I’m sure you have a bare aluminum intake (or a shiny surface...since you mentioned the heads).
I learned about this at an infrared training a few years ago.
Infrared cannot shoot through glass either.
You will get a reflection temp reading...have someone in car and roll window up and down and watch them disappear and reappear respectively.
Non-stick pans, aluminum foil, ceramic coatings will be inaccurate as well.
Something like exhaust may have to use a header wrap temporarily in a spot to get a more accurate temperature.

Might be possible that your engine is as hot as temperature gauge shows.
Hope this helps.