Spring Rate Tester: How to Measure Coil Spring Rate with a Load Cell
Reviewed by MNM Scales technicians · Updated November 3, 2026 · Prices checked November 3, 2026
Short answer: a spring rate tester measures how much force a spring pushes back with at known amounts of compression, so you can work out its rate in pounds per inch. Compress the spring to two heights, read the force at each, and divide the change in force by the change in travel. Our MNM Scales 1000 x 0.2 lb coil spring compression scale ($379) covers a wide range of coil springs, and the 250 x 0.02 lb tension and compression kit with indicator ($299) reads light springs in finer steps. Not sure which capacity fits your springs? Call (832) 290-3120.
This guide is for race teams, suspension and engine builders, spring shops and QC benches that need to check coil springs before they go on a car or into a product. MNM Scales has sold, calibrated and repaired scales for over 30 years from our shop in Cypress, Texas, and we are one of the largest scale distributors.
What a spring rate tester measures
Spring rate is the force needed to compress a spring by one unit of travel, written in lb/in or N/mm. A spring rate tester pairs a load cell, which reads the force, with a fixture that compresses the spring squarely and a way to measure how far it moved. The load cell is the part that sets accuracy: its capacity has to cover the highest force you will reach, and its resolution decides how finely you can see small changes.
- Coil springs: rate in lb/in across the working range, plus ride height loads.
- Valve springs: seat pressure at installed height and open pressure at full lift.
- Extension springs: the 250 lb and 750 lb kits are listed for tension as well as compression, so they can pull-test extension springs too. For more on pull loads, see our tension load cell guide.
How to measure spring rate step by step
- Set the spring on the load cell in a press, arbor or bench fixture that loads it straight down the center line. Off-center loading reads low and bends the spring.
- Zero the indicator with the top plate or adapter in place, so only the spring force is read.
- Compress the spring to your first height and record the force (F1) and the travel or height (x1). Use a dial indicator, height gauge or ruler on the press.
- Compress it to a second height, about two thirds of the working travel, and record F2 and x2. A third point shows whether the rate stays linear.
- Work out the rate: (F2 − F1) ÷ (x2 − x1).
- Repeat two or three times and average. Note the spring ID, heights, loads, date and the tester you used.
Example: a spring reads 180 lb at 1.000 in of compression and 540 lb at 3.000 in. The rate is (540 − 180) ÷ (3.000 − 1.000) = 180 lb/in. Measuring between two loaded points, rather than from zero, keeps the first bit of seating in the coils out of the result.
Not included: the press or fixture, the travel gauge and spring adapters are not included with the load cell kits. Tell us your spring sizes and we can help you plan the setup.
Spring rate tester models compared at live prices
| Model | Capacity x resolution | Listed for | Price |
|---|---|---|---|
| MNM Scales Coil Spring Race Car Compression Scale 250 x 0.02 lb | 250 x 0.02 lb | Compression and tension, S-type load cell + indicator | $299 |
| MNM Scales Coil Spring Race Car Compression Scale 500 x 0.1 lb | 500 x 0.1 lb | Compression, S-type load cell | $359 |
| MNM Scales Coil Spring Race Car Compression Scale 750 x 0.1 lb | 750 x 0.1 lb | Compression and tension, S-type load cell + indicator | $299 |
| MNM Scales Coil Spring Race Car Compression Scale 1000 x 0.2 lb | 1000 x 0.2 lb | Compression, S-type load cell | $379 |
| MNM Scales Coil Spring Race Car Compression Scale 2000 x 0.5 lb | 2000 x 0.5 lb | Compression, S-type load cell | $379 |
| MNM Scales Coil Spring Race Car Compression Scale 3000 x 0.5 lb | 3000 x 0.5 lb | Compression, S-type load cell | $379 |
How to pick capacity and resolution
- Capacity: take the highest rate you test, multiply by the most travel you will use, and pick a tester above that load. A 300 lb/in spring compressed 3 in reaches 900 lb, so the 1000 lb model fits.
- Resolution: finer steps matter on light springs. The 250 x 0.02 lb kit shows 0.02 lb steps; the 500 x 0.1 lb and 750 x 0.1 lb models read in 0.1 lb steps.
- Heavy springs: stiff coil-over and spring-stack work moves to the 2000 x 0.5 lb or 3000 x 0.5 lb models.
- Matched sets: testing every spring in a set on the same tester, at the same heights, gives the cleanest side-to-side comparison.
Peak hold and data output on the indicator kits
The 250 lb and 750 lb kits are listed with an indicator (SKU MSLP7515). On the LP7515 indicator, the Hold setting gives peak hold (1), data hold (2) or auto hold (3), so you can freeze the force at a set height before you write it down. The trn and bAud settings send readings over RS-232 to a PC or printer. See our LP7515 indicator settings guide for the menu steps.
Weighing up a spring tester against other force tools? Our guide to compression scales, force gauges and load cells explains where each one fits.
Rules: records and NTEP
Spring rate testers measure force for setup and quality checks. Keep a simple record for each spring: ID, test heights, loads, calculated rate, date and the tester’s calibration date, so results can be compared over time. For anything you sell by weight, see our NTEP guide.
Texas note: TDA does not require an NTEP certificate for every device, but the scale must meet NIST Handbook 44 and suit its use; some scales do need one, so we recommend NTEP models and can check yours. See TDA’s scales used in trade guidance (PDF) and our TDA scale certification guide, or call us or TDA to confirm your use.
Calibration and rental
- Testers up to 150 kg (the 250 lb model): in-house calibration with a certificate or NIST calibration with a NIST-traceable certificate; call us for a quote. See NIST vs in-house certificates.
- Testers over 150 kg (500 lb and up): in-house calibration with a certificate or NIST calibration with a NIST-traceable certificate; call (832) 290-3120 for pricing.
- On-site service: $295 + $2 per mile per visit across the Houston area, with calibration charged per device; see our industrial scale calibration service and on-site calibration.
- Mail-in, repairs and rentals: ship testers for mail-in calibration, have us repair the brands we sell, and rent all types of scales while yours is out of service.
Setting up a spring rate tester? Tell us the springs you test, their highest rate and travel, and we will match a capacity and quote calibration. Shop: 21249 FM 529 Rd, Cypress, TX 77433, visits by appointment.
Frequently asked questions
How do you calculate spring rate?
Read the force at two compressed heights and divide the change in force by the change in travel: (F2 − F1) ÷ (x2 − x1). The answer is in lb/in when force is in pounds and travel in inches.
What capacity spring rate tester do I need?
Multiply the highest spring rate by the most travel you will test, then pick a tester above that load. A 300 lb/in spring compressed 3 in needs at least 900 lb, so a 1000 lb tester fits.
Can a spring rate tester check valve springs?
Yes. Read seat pressure at installed height and open pressure at full lift. The 250 x 0.02 lb kit reads lighter loads in fine steps, and the 500 lb and 750 lb models cover higher open pressures.
Can I test extension springs?
Yes, with the 250 lb or 750 lb kits, which are listed for tension as well as compression.
Is the press or travel gauge included?
No. The press or fixture, travel gauge and spring adapters are not included with the load cell kits.
Can you calibrate a spring rate tester?
Yes. We calibrate in-house with a certificate, by mail-in and on-site across Houston. Call (832) 290-3120 for a quote for your tester.