Spring Rate Conversion Guide: lb/in to kg/mm & kg/mm to lb/in

Understanding spring rates is essential for tuning your suspension for the perfect balance of performance, comfort, and handling. Choosing the right rate depends on your car, driving style, and the purpose of the vehicle that you’d like to optimize.

Fortune Auto Premium Chrome Silicon Springs

Swift Springs 60mm ID

Swift Spec-R Lowering Springs

Fortune Auto SuperLow Springs

What is Spring Rate?

Spring rate refers to how much force is needed to compress a spring by a given distance.

1kg/mm = 55.997 lb/inch

lb/in (Pounds per Inch) – Measures how many pounds of force are required to compress the spring by 1 inch.
kg/mm (Kilograms per Millimeter) – Measures how many kilograms of force are required to compress the spring by 1 millimeter.

Why is Conversion Important?

Different suspension manufacturers use different units of measurement. If you’re switching between brands or trying to match a specific setup, it’s important to accurately convert spring rates to ensure proper suspension tuning.

To make it easy, we’ve provided a handy spring rate conversion chart below. Simply find your known spring rate, and use the table to determine the equivalent value in the other unit.

KG/mm to LB/in

Spring Rate (kg/mm)	Spring Rate (lb/in)
4k	224 lb/in
5k	280 lb/in
6k	336 lb/in
7k	392 lb/in
8k	448 lb/in
9k	504 lb/in
10k	560 lb/in
11k	616 lb/in
12k	672 lb/in
13k	728 lb/in
14k	784 lb/in
15k	840 lb/in
16k	896 lb/in
17k	952 lb/in
18k	1008 lb/in
20k	1064 lb/in
22k	1120 lb/in
24k	1344 lb/in
26k	1456 lb/in
28k	1568 lb/in
30k	1680 lb/in
32k	1792 lb/in
34k	1904 lb/in
38k	2128 lb/in
42k	2352 lb/in
46k	2576 lb/in
50k	2800 lb/in

LB/mm to KG/in

Spring Rate (lb/in)	Spring Rate (kg/mm)
300	5.4
350	6.3
400	7.1
450	8.0
500	8.9
550	9.8
600	10.7
650	11.6
700	12.5
750	13.4
800	14.3
850	15.2
900	16.1
950	17.0
1000	17.9
1100	19.6
1200	21.4
1300	23.2