Accomodation
The physical setting and other furniture pieces in the room where the finished work will be displayed also have a bearing on sizing. For example, the number of books to be held as well as the footprint influenced how I sized a credenza for storage purposes and how I picked the style of doors.

Form follows function. Storage needs and footprint restrictions took priority in this credenza's design.
When in Doubt, Just Build a Mock-Up
The basic sketch and cutlist are usually enough for me. However, two-dimensional drawings don't always capture the full complexities or hidden aspects of a project such as comfort or joinery strength. A quick prototype or mock-up is another tool at your disposal. Here are a few illustrations of how mock-ups can help.
Start With the Template
Mock-ups can exist in different forms: scaled, full size, for the whole build or just for one part. When I designed an oval-top coffee table for my daughter, I made a few different prototypes of just the top (Built to Last – Coping with Wood Movement). The cardboard mock-up enabled her to see how each design and the size of the top looked relative to the other pieces at her place. The finalized tabletop mock-up served two functions: to trace out the shape for cutting and to help determine the positions (and mortise placements) for the legs.

Left: Mock-ups can be scaled or full-size, or, in this case, be just one part (the top) of the furniture.
Middle: The author used the tabletop template to help figure out the placement of boards for jointing.
Right: The author positioned the legs on the template to determine the mortise placements for them.
Use Mock-Ups to Work Out the Details
I also use mock-ups to help me nail down final details or to test assumptions. For a step stool, for example, I came up with a concealed-pin system made out of a few hardware supplies to hold the swing step to the stool body. But would the pin hold up to real-life use? To find out, I made a scaled mock-up of the swing step and repeatedly stood on it to stress-test the pin hinges. For the same project, I also used a mock-up template of the step support to determine the drilling locations for the pins.

Left: The stool has a hinged step that can be swung out when needed.
Right: Using a mock-up, the pin-hinge system was stress-tested with the standing weight of an adult.

A full-size template of the step leg allowed the author to figure out the drill hole location for the pin with ease.
Mock-Ups Help Prevent Disasters
While the advice of "Measure Twice, Cut Once" reduces cutting blunders, I need an assurance that calculated measurements for critical parts are indeed correct and precise before cutting them. For instance, the sliding doors for the credenza had to be trimmed correctly to work with the door tracks in the carcass. I took no chances and before milling the doors to size, I made a mock-up of each door and test fit it on each track.

Left: The author cut two cardboard doors based on the calculated size and used them to confirm the accuracy of the calculation.
Right: He trimmed the doors after the mock-up exercise.
Angles For Dummies
Unlike linear measurements, angles or elevations are harder to visualize on paper relative to the actual setting. So, to figure out the cut angle for a nook table's raised feet, I milled a few boards at different angles as mock-up legs. I held one mock-up at a time to the table pedestal to see which angle gave the most pleasing look. Similarly, I used mock-ups to work out the angled legs for the credenza base.

Left: The author determined the angle of cut for this table's feet without using any calculations.
Right: Holding a mock-up foot to the pedestal allowed the author to see the actual elevation of the foot relative to the floor.
Mock-ups, made of simple supplies such as cardboard, foam insulation or scrap wood, can help you tackle various design challenges. They are truly a woodworker's "undo" button and allow for design experimentation without fear of failure.
Text and photos by Charles Mak
Charles Mak is a businessperson and enthusiastic hobby woodworker, teacher, writer and tipster. He formerly worked part-time at his local Lee Valley Tools store.
Further Reading
Blackburn, Graham. "A Guide to Good Design". Fine Woodworking. Jan./Feb. 2004. p. 48 - 51.
Gilpin, Hank. "The Illustrated Cutlist". Fine Woodworking. Jan./Feb. 2019. p. 55 - 59.
Hayward, Charles. Accommodation and Proportion. The Woodworker: The Charles H. Hayward Years. Vol. II. The Lost Art Press. 2016. p. 775 - 776.
Lauer, George. "James Krenov: Practical Lessons from a Renowned Master". Wood magazine. September 2002. p. 68 - 72.