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Cell size

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Cell Size is an XTerm window manipulation sequence that queries the pixel dimensions of an individual character cell in the terminal.

Syntax​

CSI 16 t                       Request cell size in pixels
CSI 6 ; height ; width t       Response: cell pixel dimensions
Formal syntax
(* Request *)
cell_size_request  = 0x1b, "[", "1", "6", "t" ;

(* Response *)
cell_size_response = 0x1b, "[", "6", ";", Pn, ";", Pn, "t" ;
Pn                 = digit, { digit } ;
digit              = "0" | "1" | "2" | "3" | "4"
                 | "5" | "6" | "7" | "8" | "9" ;

Response​

FieldDescription
heightHeight of a single character cell in pixels
widthWidth of a single character cell in pixels

Description​

This sequence queries the terminal for the pixel dimensions of a single character cell. It is part of the XTerm CSI Ps ; Ps ; Ps t window manipulation family.

When the terminal receives CSI 16 t, it responds with CSI 6 ; height ; width t where height and width are the pixel dimensions of a single character cell. The cell size is determined by the current font and its rendering configuration.

Typical cell sizes for common monospace fonts are in the range of 7-10 pixels wide by 14-20 pixels tall, though high-DPI displays and font scaling can produce larger values.

The cell size report is particularly useful for:

  • Graphics protocols: Applications that render inline graphics (such as Sixel or Kitty Graphics) need the cell size to correctly scale images to align with the character grid.
  • Size calculations: Dividing the Text Area Size (pixels) by the cell size yields the text area dimensions in characters.
  • Mouse position mapping: Converting pixel-based mouse coordinates to character cell positions.

Examples​

# Query cell size
printf '\e[16t'

# Read the response
printf '\e[16t'; read -st 1 -d t response; echo "$response"

Specifications​

SpecificationSection
XTerm ctlseqs—

Terminal support​

TerminalSupportVersionNotes
Terminal Emulators
Alacritty✗NoExplicitly rejected - CSI 16 t not in supported list (escape_support.md line 81-82)
Bobcat✓0.9.0Requires WindowReports enabled in profile
contour✓v0.1.0
foot✓YesImplemented at csi.c:1347-1354, reports cell height and width in pixels
Ghostty✓v1.0.0
iTerm2✗NoNot implemented. Parser explicitly marks Ps=16 as VT100_NOTSUPPORT. Delegate method terminalCellSizeInPoints exists but is not connected to this sequence.
Kitty✓YesReports cell size in pixels via CSI 6;height;width t
Konsole✓YesReports cell size in pixels via CSI 6 t response
mintty✓YesReports cell dimensions via CSI 16 t, implemented in src/termout.c:3045
mlterm✓rel-3_8_6
PuTTY✗NoNot implemented; CSI t handler only includes cases 1-21 (excluding 10,12,15,16,17)
Rio✓v0.1.11
rxvt-unicode✗NoNot implemented; fwidth/fheight available internally but no CSI 16 t handler
st✗No
terminology✗No
VT100✗No
VTE✗NoCSI 16 t not implemented; VTE skips from operation 14 to 18 in XTERM_WM enum
WezTerm✓YesFully implemented in term/src/terminalstate/mod.rs:2035-2045
Windows Terminal✓YesImplemented as ReportCharacterCellSize in WindowManipulationType enum (value 16)
xterm✓xterm-406Requires OPT_MAXIMIZE compile flag (enabled by default)
xterm.js✓4.4.0Requires windowOptions.getCellSizePixels to be enabled
Multiplexers
cy✗NoCSI t (XTWINOPS) explicitly ignored since v0.1.0
GNU Screen✗NoCSI 16 t not implemented; only CSI 7/8/11/18/21 t are handled
tmux✓3.4Reports cell size in pixels via w->xpixel and w->ypixel
tuios✓v0.2.2
Zellij✓v0.28.0

See also​