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Accurately Determining Moulding Needs

Sometimes you need to know down to the 1/16" how much moulding is required to make a frame or rail for a frame. Since most often you are dealing with the Frame Dimension the actual length you need will be greater than the measurements you have written down.

First there is some data you will need to collect:

  • The width of the moulding (W)
  • Rabbet width (R) − not height
  • The amount of material lost between pieces on your chopper or saw (C)
  • Allowance amount (A)
  • Dimension1 (D1) and Dimension2 (D2)

Using the above definitions, follow the directions below to determine the number of inches needed.

Frame Dimension
One Frame: ((D1 + D2) • 2) + (((WR) • 2 + A) • 4) + (3 • C)
One Rail: (WR) • 2 + A + (D1 or D2)
Sight Size
One Frame: ((D1 + D2) • 2) + ((W • 2 + A) • 4) + (3 • C)
One Rail: (W • 2) + (D1 or D2)
Outside Size
One Frame: ((D1 + D2) • 2) + (3 • C)
One Rail: (D1 or D2)

In all cases you will need to figure out how much you need to trim off the end(s) to accommodate any splits, dings, etc.