Why the size matters for school projects
School projects are usually specified as "one full chart paper". Printing something close and trimming it down looks obviously wrong next to a classmate who used a real sheet. Setting the size to 56 × 71 cm and printing to that exact figure gives you a poster that matches the brief.
If your school uses half chart, set 56 × 35.5 cm instead — the tool takes any size you type.
What it costs in sheets
About nine A4 sheets in a 3 × 3 grid, once you allow for the margin your printer cannot reach and the flap that gets glued under the next sheet. The exact count is on screen before you download anything, and it updates live as you change the size.
On A3 paper the same poster comes down to about six sheets, which means far fewer joins to tape.
Printing it at school or at a shop
The PDF is built on your device, so you can carry it on a phone and send it to a print shop over WhatsApp. Tell them to print at 100% and not to fit to page — that one setting is the difference between sheets that line up and sheets that do not.
Every sheet is numbered on the printout, and page one is an assembly map showing where each number goes.
Diagrams and text stay readable
A diagram drawn for a screen has far fewer pixels than a chart-paper poster needs. The quality meter shows the real DPI at the size you have chosen and warns you before you commit paper to something that will print soft.
For hand-labelled work, printing the artwork and writing the labels on afterwards usually looks better than blowing up small text.