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Leaf Spring Calculator



Spring Rate is half the difference between the loads 1 inch above and 1 inch below a specified position. Another definition would be: The amount of force it takes to compress the spring 1-inch and is expressed in ld/in.  The lower the rate, the softer the spring.  If the front of your truck is sagging you need more spring load, not more spring rate.

Spring Load is the amount of weight the spring is designed to carry at a certain height. This is also called the Design Load or Load Rate.  Think weight carrying capacity.

Load Rate is not to be confused with Spring Rate.  Load Rate is the amount of weight a spring is designed to carry at a certain height.

Let's say a spring has:

  • A rate of 200 lb/in

  • Designed for a 3-Inch deflection

  • When deflected 3-inches the spring is supporting 600 lbs

  • Therefore, the spring has a Load Rate of 600 lbs.  Not a Spring Rate of 600 lbs.

Unsprung Weight is the weight of the tires, wheels, knuckles, hubs, axles, and half the weight of the springs, shocks, control arms, and/or links.

Sprung Weight is the weight of the body, chassis, drivetrain, tools, parts and the other half of the total weight of the springs, shocks, control arms and/or links.

Wheel Rate is the spring rate actually measured at the wheel (or tire).  The wheel rate is usually lower than the true spring rate due to factors such as spring position and control arm or axle leverage that can effectively lessen the spring rate at the wheel versus the actual spring rate at the spring.  If you move the spring closer to the tire (and the spring travels parallel to the wheel), the wheel rate and spring rate will become almost the same.

Variable Rate Springs have a soft initial spring rate and to absorb the subtle irregularities of the road/trail progressing to a firmer rate to handle large bumps.  These springs increase in rate as they are compressed.

Effect On Rate:

In the formula below you will see Number of Leaves, Leaf Length, Leaf Width, and Leaf Thickness.  Here is how they effect rate:

Dimension Increased

Effect On Rate
Number of Leaves Higher
Leaf Length Lower
Leaf Width Higher
Leaf Thickness Higher



Leaf Spring Rate Calculator

For Inch To Decimal Chart, Click HERE

Number of Leaves:


Thickness of Main leaf:


Length of Main Leaf:


Width of Main Leaf:


Check if leaf ends are tapered/diamond cut:

(Spring rate calculation shown at bottom)

SPRING RATE is a measure of the force required to compress a spring one inch. Spring rate is usually expressed using ft/lbs-in. Enter all values using inches and fractions of inches. Convert the fractions to decimal. For example: 2 1/2 inches should be input as 2.5 inches.

Leaf spring rates are determined primarily by the length, number, width, and thickness of the leaves in a spring pack. But other factors, such as if the leaf ends are tapered or diamond cut, can impact a spring rate. Also the effective spring rate or "feel" can be impacted by spring eye bushing design, and whether or not anti-friction material is used between the leaves. This calculator takes into account the major factors effecting spring rate and assumes a standard spring design. Accuracy will diminish when spring designs fall outside the norm.

If you already know your official factory spring rates, and have an opportunity to use this calculator, then I would be interested to here from you on how close the calculated spring rate is to your factory designated rates.

(Spring Rate Will Be Displayed Below)