merge numbers spreadsheets

Formulas in one Numbers document cannot refer to cells in a separate document. But good old copy-paste works well. Select cells in a table in one document, command-c to copy, click in the document where you want to consolidate the document and command-v to paste.

You can also move an entire sheet (tab) at a time. Select Copy Sheet in the dropdown by the sheet name in the tab at the top. Switch to the destination document and select Paste Sheet from the dropdown of any existing sheet.

Or you can move an entire table at a time by selecting it, clicking the concentric circles "bull's-eye" at it upper left, command-c to copy it as an object, click on the canvas of a sheet in the destination document, and command-v to paste.

Once you've got your data in one document you can manipulate via formulas if needed.

SG

To copy everything over from one document to another, you can copy it over sheet by sheet as explained by SGIII. However, if you have tables/charts on one sheet that refer to tables on another sheet, you will first have to consolidate them into one sheet before making the copy/paste transfer to the other document. To do that,

1. Go to one of the sheets
2. Command A to copy all
3. Command X to cut
4. Go to the other sheet . Ignore any error triangles you see, they will repair themselves when you paste the tables back in during the next step
5. Paste.
6. It will likely paste it right on top of everything else so, before clicking off (deselecting) what you just pasted, drag it all downward or to the right until it is no longer overlapping. Note that any tables of the same name will be given a -1 after the name.

When you get this consolidated sheet pasted into the new document you can split it back up into separate sheets using Cut and Paste.

This same idea applies if you are going to copy/paste tables, not entire sheets, to the new document. Tables and charts that reference each other must be consolidated onto one sheet so they can be selected together for the copy/paste to another document.

By "merge" do you mean get a sum of 2 or more numbers?

Remember, this a spreadsheet number cruncher; you don't actually merge, you sum. Or subtract, divide or multiply or some other function.

Formulas and Functions Help - Apple Support

For two different sheets you have to designate the sheet one cell plus the sheet two cell.

You likely will get better service here: Numbers - Apple Community

There re also numerous Numbers tutorials.

You consolidate cell by cell as far as I know. But you can create a formula that replicates a math function while one or more variables stays the same and those cell references are not changed, i.e. maintaining fixed cell references and varying another. It helps if all the spread sheets the the same exact configuration or your fixed cell references will be off.

You really need to discuss this ins the Numbers forum. I've been an Excel power user for a couple of decades ... going back to VisiCalc as a start. They all work similarly with each brands own quirks, but the learning curve is often quite steep..

https://smallbusiness.chron.com/add-cells-across-multiple-spreadsheets-44275.html

Note it's adding cells across multiple sheets. The process for Numbers should be very similar.