Conversion factors between mapping scales and lengths/areas.
Scale 1:X	feet/inch(ft/in)	inch/mile(in/mi)	m/cm(m/cm)	cm/km(cm/km)	acres/sq. inch(acres/in²)	sq. miles/sq. inch(mi²/in²)	m²/cm²(m²/cm²)
1	0.083	63398	0.01	100000	1.6e-7	2e-10	0.0001
2	0.167	31699	0.02	50000	6.4e-7	1e-9	0.0004
5	0.417	12680	0.05	20000	0.00000399	6.2e-9	0.0025
10	0.833	6340	0.1	10000	0.00001594	2.49e-8	0.01
20	1.67	3170	0.2	5000	0.000064	1e-7	0.04
50	4.17	1268	0.5	2000	0.000399	6.2e-7	0.25
75	6.25	845	0.75	1333	0.000897	0.0000014	0.563
100	8.33	634	1	1000	0.00159	0.0000025	1
150	12.5	423	1.5	667	0.00359	0.0000056	2.25
200	16.7	317	2	500	0.00638	0.00001	4
250	20.8	254	2.5	400	0.00996	0.0000156	6.25
300	25	211	3	333	0.0143	0.000022	9
400	33.3	158	4	250	0.0255	0.00004	16
500	41.7	127	5	200	0.0399	0.000062	25
1000	83.3	63	10	100	0.159	0.000249	100

Source: engineeringtoolbox.com

Examples

Example: Scale 1:100

The scale of a drawing is 1:100. From the table, the conversion factor is $1.0 \text{ m/cm}$ . $1 \text{ cm (drawing)} \times 1.0 \text{ m/cm} = 1 \text{ m (real)}$

Example: Scale 1:10000

The scale of a map is 1:10000. From the table, the conversion factor is $0.1 \text{ km/cm}$ . $1 \text{ cm (map)} \times 0.1 \text{ km/cm} = 0.1 \text{ km (real)}$

Example: Converting a Rate

A rate of $0.1 \text{ miles/inch}$ corresponds to:

A scale of approximately *1:6300
A conversion factor of approximately 63 m/cm

Interactive Charts

Mapping scales - Converting table length and area

References

Original Source

Source: engineeringtoolbox.com