Comment 4 for bug 1834290

Using the EDID data your monitor reports in the Xrandr.txt attachment above I get the same answer
of 60x34cm so that is what the hardware is advertising itself as. Indeed that would make it 27.15 inches diagonal.

So this is a bug IN your hardware, sorry. You might be able to get a firmware update from LG. Most likely they are using the same firmware in their 27" monitors and forgot to change the dimensions for your 43" model.

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EDID version: 1.4
Manufacturer: GSM Model 23305 Serial Number 259449
Made in week 3 of 2019
Digital display
10 bits per primary color channel
DisplayPort interface
Maximum image size: 60 cm x 34 cm
Gamma: 2.20
DPMS levels: Standby
Supported color formats: RGB 4:4:4, YCrCb 4:4:4, YCrCb 4:2:2
Default (sRGB) color space is primary color space
First detailed timing includes the native pixel format and preferred refresh rate
Color Characteristics
  Red: 0.6523, 0.3349
  Green: 0.3046, 0.6367
  Blue: 0.1484, 0.0615
  White: 0.3134, 0.3291
Established Timings I & II
    640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (DMT)
    800x600 60.317 Hz 4:3 37.879 kHz 40.000 MHz (DMT)
   1024x768 60.004 Hz 4:3 48.363 kHz 65.000 MHz (DMT)
Standard Timings
   1152x864 59.959 Hz 4:3 53.783 kHz 81.750 MHz (EDID 1.4 source: CVT)
   1152x864 60.000 Hz 4:3 53.700 kHz 81.624 MHz (EDID 1.3 source: GTF)
   1280x1024 60.020 Hz 5:4 63.981 kHz 108.000 MHz (DMT)
   1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (DMT)
   1600x900 60.000 Hz 16:9 60.000 kHz 108.000 MHz (DMT, RB)
   1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (DMT)
   1280x800 59.810 Hz 16:10 49.702 kHz 83.500 MHz (DMT)
Detailed mode: Clock 533.250 MHz, 600 mm x 340 mm
               3840 3888 3920 4000 ( 48 32 80)
               2160 2214 2219 2222 ( 54 5 3)
               +hsync -vsync
               VertFreq: 59.997 Hz, HorFreq: 133.312 kHz
Detailed mode: Clock 266.640 MHz, 600 mm x 340 mm
               3840 3848 3992 4000 ( 8 144 8)
               2160 2214 2219 2222 ( 54 5 3)
               +hsync -vsync
               VertFreq: 30.000 Hz, HorFreq: 66.660 kHz
Display Range Limits
  Monitor ranges (GTF): 56-61 Hz V, 30-135 kHz H, max dotclock 560 MHz
Display Product Name: LG Ultra HD
Has 1 extension block
Checksum: 0x2a

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CTA-861 Extension Block Revision 3
Basic audio support
Supports YCbCr 4:4:4
Supports YCbCr 4:2:2
1 native detailed modes
13 bytes of CTA data blocks
  Video Data Block
     1920x1080 60.000 Hz 16:9 67.500 kHz 148.500 MHz (VIC 16, native)
     1280x720 60.000 Hz 16:9 45.000 kHz 74.250 MHz (VIC 4)
      720x480 59.940 Hz 16:9 31.469 kHz 27.000 MHz (VIC 3)
      640x480 59.940 Hz 4:3 31.469 kHz 25.175 MHz (VIC 1)
  Audio Data Block
    Linear PCM, max channels 2
      Supported sample rates (kHz): 48 44.1 32
      Supported sample sizes (bits): 24 20 16
  Speaker Allocation Data Block
    Speaker map:
      FL/FR - Front Left/Right
Detailed mode: Clock 148.500 MHz, 600 mm x 340 mm
               1920 2008 2052 2200 ( 88 44 148)
               1080 1084 1089 1125 ( 4 5 36)
               +hsync +vsync
               VertFreq: 60.000 Hz, HorFreq: 67.500 kHz
Detailed mode: Clock 241.500 MHz, 600 mm x 340 mm
               2560 2608 2640 2720 ( 48 32 80)
               1440 1443 1448 1481 ( 3 5 33)
               +hsync -vsync
               VertFreq: 59.951 Hz, HorFreq: 88.787 kHz
Checksum: 0xc8