Your question isn't very specific, so here is a generic example from another question

From the documentation for ImageSize:

The following settings can be given:

72di di inches (before magnification)

Suppose we want to give sizes in centimeters. We establish a scale:

cm = 72/2.54;

And we give the ImageSize in this scale, also making sure to set PlotRangePadding -> None. This gives a 1cm x 1cm orange square on a 19cm x 28cm field.

g = Graphics[{Rectangle[{0, 0}, {19, 28}], Orange, 
    Rectangle[{0, 0}, {1, 1}]}, PlotRangePadding -> None, 
   ImageSize -> {19, 28}*cm];

When exporting you can give a specific resolution to use. For printing 300dpi may be appropriate:

Export["print.tif", g, ImageResolution -> 300]

Your question isn't very specific, so here is a generic example from another question

From the documentation for ImageSize:

The following settings can be given:

72di di inches (before magnification)

Suppose we want to give sizes in centimeters. We establish a scale:

cm = 72/2.54;

And we give the ImageSize in this scale, also making sure to set PlotRangePadding -> None. This gives a 1cm x 1cm orange square on a 19cm x 28cm field.

g = Graphics[{Rectangle[{0, 0}, {19, 28}], Orange, 
    Rectangle[{0, 0}, {1, 1}]}, PlotRangePadding -> None, 
   ImageSize -> {19, 28}*cm];

When exporting you can give a specific resolution to use. For printing 300dpi may be appropriate:

Export["print.tif", g, ImageResolution -> 300]

Your question isn't very specific, so here is a generic example from another question

From the documentation for ImageSize:

The following settings can be given:

72di di inches (before magnification)

Suppose we want to give sizes in centimeters. We establish a scale:

cm = 72/2.54;

And we give the ImageSize in this scale, also making sure to set PlotRangePadding -> None. This gives a 1cm x 1cm orange square on a 19cm x 28cm field.

g = Graphics[{Rectangle[{0, 0}, {19, 28}], Orange, 
    Rectangle[{0, 0}, {1, 1}]}, PlotRangePadding -> None, 
   ImageSize -> {19, 28}*cm];

When exporting you can specify a specific resolution to use. For printing 300dpi may be appropriate:

Export["print.tif", g, ImageResolution -> 300]

Your question isn't very specific, so here is a generic example from another question

From the documentation for ImageSize:

The following settings can be given:

72di di inches (before magnification)

Suppose we want to give sizes in centimeters. We establish a scale:

cm = 72/2.54;

And we give the ImageSize in this scale, also making sure to set PlotRangePadding -> None. This gives a 1cm x 1cm orange square on a 19cm x 28cm field.

g = Graphics[{Rectangle[{0, 0}, {19, 28}], Orange, 
    Rectangle[{0, 0}, {1, 1}]}, PlotRangePadding -> None, 
   ImageSize -> {19, 28}*cm];

When exporting you can give a specific resolution to use. For printing 300dpi may be appropriate:

Export["print.tif", g, ImageResolution -> 300]