A hard cost rate that reads correctly in metres and reads wrong in feet is worse than no number at all. Spreadsheet keeps every project number honest whether your project runs in metric or imperial.
Metric and imperial units
Giraffe's own numbers are always metric internally. Spreadsheet reads your project's unit setting and converts numbers on their way into a cell, so the sheet matches what the rest of the project already shows.
Use the Units control in the toolbar to choose how the sheet displays numbers:
Units: project: follows the project's own setting. This is the default.
Units: metric: always metres and square metres, regardless of the project setting.
Units: imperial: always feet and square feet, regardless of the project setting.
Switching this control converts every cell on the sheet in place. Typing a value back into the project always sends it in metric, whatever the sheet displays.
A rate converts the other way from an area. $8,700 per square metre is $808 per square foot, so multiplying an area by a rate gives the same money in either system.
The Blocks sheet is never converted, because its columns are ones you invented, and Spreadsheet has no way to know which of them are areas. See The Blocks Sheet in Spreadsheet for what that sheet is for. A formula can also read which system is active with =GI.UNITS().
See The Usages Sheet in Spreadsheet for editing the rates these conversions apply to, and Importing a Workbook in Spreadsheet for bringing in a workbook built in a different unit system.