While the format of your report is not as important as the content, here are some best practices to follow:

• Font size of 11 or 12 is acceptable
• Most applications will default to 1" margins and is acceptable
• Spacing is not a top concern, though if possible stick to either 1.15 or double spacing
• Your lab report is expected to be 2-3 pages of text to cover everything sufficiently; 4+ pages of text is fine, though unnecessary (unless your report is double-spaced)