If you want to know the scale factor(ratio) between two lengths, try this,scale factor calculator, It helps us calculate the scale ratio more easily.

This is an online scale length converter that calculates the actual length and the scale length according to the scale ratio. scale ratio could be set by yourself, supports different length units, including imperial units and metric units. With visual graphic and formula, it let us more easily understand the calculation process and the result.

- Set the scale ratio according your need, eg 1:10, 1:30, 35:1
- Select the unit of real length and scale length
- Using different units will automatically convert the result
- Enter the number of real length, the scale length will be calculated automatically.
- Enter the number of scale length, the real length will be calculated automatically.

To calculate the
*scale length*, use real length multiply the scale factor of it, then divide the scale factor of scale length, for example

Scale length : 240 inch × 1 ÷ 12 = 20 inch

Scale ratio 1:12

Real length : 240 inch
Scale length : 240 inch × 1 ÷ 12 = 20 inch

Room scale size at scale 1:100

A room of 5.2 meters by 4.8 meters, what is the scale size for the building plan at scale 1:100 ?
First, we can convert the unit from meter to centimeter.

5.2 m = 5.2 × 100 = 520 cm

4.8 m = 4.8 × 100 = 480 cm

Then, convert by scaling

520 cm × 1 ÷ 100 = 5.2 cm

480 cm × 1 ÷ 100 = 4.8 cm

So we have to draw a room of 5.2 x 4.8 cm

To calculate the
*real length*, use scale length multiply the scale factor of it, then divide the scale factor of real length, for example

Real length : 5 cm × 200 ÷ 1 = 1000 cm

Scale ratio 1:200

Scale length : 5 cm
Real length : 5 cm × 200 ÷ 1 = 1000 cm

Door actual width at scale 1:50

On the building plan the width of the front door is 18.6 mm.
and the scale of the plan is 1:50,

what is the actual width of that door ?

First, we convert the unit from millimeter to centimeter.

18.6 mm = 18.8 ÷ 10 = 1.86 cm

Then, convert by scaling

1.86 cm × 50 ÷ 1 = 93 cm

So the actual width of door is 93 cm