What does scale 1:1 mean?
Scale 1:1 means the drawing, print or model has the same dimensions as the real object. The first number is the size on the drawing and the second is the size in reality. They are equal, so 1 inch on paper is 1 inch on the part, and a 3 in bolt is drawn 3 in long.
The same thing goes by several names. Drafters write "full size" or "full scale", print dialogs say "actual size" or 100%, and prop builders say "life-size". On US architectural drawings it is noted as 12" = 1'-0".
Every other scale sits on one side of 1:1. Enlargement scales such as 2:1 or 5:1 draw the object bigger than it is, which helps with small parts. Reduction scales such as 1:2, 1:5 or 1:100 draw it smaller, so a cabinet or a whole building fits on a sheet.
The scale factor is 1. You do not multiply or divide anything and only have to keep the units straight: 1 ft is 12 in, and 2.5 cm is 25 mm.
Where is scale 1:1 used?
People work at 1:1 when the object fits on the sheet and they want to lay a real part on the drawing or trace a shape without converting anything:
- Technical drawings. Small parts such as bolts, bushings and brackets are drawn full size as long as they fit on the sheet. ISO 5455 lists 1:1 between enlargement scales such as 2:1, 5:1 and 10:1 and reduction scales such as 1:2, 1:5 and 1:10.
- Sewing patterns. You print a pattern at 1:1, tape the pages together and pin it straight onto the fabric.
- Woodworking and DIY templates. A drilling template or a curve pattern is taped to the workpiece, and you cut or drill along the lines.
- Electronics. A 1:1 printout of a circuit board lets you set the components on the paper and check the pin spacing before you order the board.
- Architectural details. Moldings and joints are sometimes drawn full size so the profile can be checked against the real piece.
- Life-size replicas. A 1:1 scale prop, helmet or car replica is the size of the original.
Scale 1:1 in practice: examples
A few sizes you can check with a ruler:
- A credit card is 3.37 × 2.125 in (85.6 × 54 mm). Drawn at 1:1 it has the same size, so you can hold a card against a printout to check that the printer did not resize the page.
- A Letter sheet is 8.5 × 11 in. A 10 in part fits on it at 1:1 along the long side. A 15 in part does not and needs a Tabloid sheet (11 × 17 in).
- A 60 × 30 in desk top is longer than an ANSI E sheet (34 × 44 in). That is why furniture is usually drawn at a reduction scale such as 1:12.
- A detail 0.25 in long is hard to read at 1:1. At 4:1 it is 1 in long on the drawing and leaves room for dimensions.
- A TV mount with a VESA 200 × 200 pattern has holes 200 mm apart, about 7.87 in. On a 1:1 template the distance is the same, so you tape the paper to the wall and drill through it.