Is there a standard paragraph indentation for novels, in terms of inches or centimeters?Yes. It's called a "span", and a person who employs this paragraph technique is a "spanner". If you use it throughout your novel, you're known in the publishing industry as a "complete spanner". Complete spanners measure their paragraph "span" by placing their middle finger over the screen between the text and white space at the start of the paragraph when Word magnification is at 128.25% using Tahoma font.
You can stare at your middle finger and draw a virtual line across the screen with the index finger of your free hand until it touches the far edge of the screen. Then, trace your eyeline back to the middle finger and focus on it. Once you're happy, think about writing your manuscript, rather than considering what a complete spanner you are.