ASTM International
Standard Specification for Steel Wire, Carbon, for Springs
ASTM A229 Standard
Coil Gauge Firmness: 13.75 vs 14.5 vs 15 AWG
Metallurgical mechanics: deflection constants, spring rates, and how a 0.5-gauge difference alters perceived firmness from plush to firm.
Exponential Stiffness Differences in AWG
Direct answer summary
Wire gauge numbers follow an inverse logarithmic scale: smaller numbers represent thicker wire with exponentially higher deflection resistance. A 13.75 AWG coil uses 2.05 mm steel wire, creating a rigid, firm spring rate (> 1.6 lbs/in deflection resistance) ideal for heavy sleepers. A 14.5 AWG coil uses 1.83 mm wire, delivering universal medium-firm support (~1.2 lbs/in). A 15.0 AWG coil uses 1.65 mm wire, producing compliant plush contouring (~0.8 lbs/in) for side sleepers.
Key points
13.75 AWG (2.05 mm): High spring rate (>1.6 lbs/in), creating firm orthopedic support.
14.5 AWG (1.83 mm): Universal medium-firm spring rate (~1.2 lbs/in) for combination sleepers.
15.0 AWG (1.65 mm): Plush compliant spring rate (~0.8 lbs/in) that cushions side sleeper shoulders.
Interactive example
Explore an example related to this answer.
3D Layer-Peel Visualizer
Interactive Visual Tool
Interactive Exploded Architecture & Layer Inspection
Peel through the physical mattress assembly to audit coil gauge, foam density (PCF), indentation load deflection (ILD), and flame barrier composition.
What's insideDrawing only, layer order not confirmed
Wire Diameter & Spring Rate Comparison layers
Height: 8.00"
Layers: 1 Layers
1/1
All
Active Layer: Pocket Spring Wire
8" (CORE)Thickness: 8"Material: High-Tensile Carbon SteelGauge: 14.5 AWGCoils: 5-Zone (14.75 / 15.5 AWG)
Layers, top to bottom (1)
Click to expand specs13.75 AWG (Firm), 14.5 AWG (Medium), 15.0 AWG (Plush)
Thickness8 inches100.0% of stack
MaterialHigh-Tensile Carbon Steel
Coil Wire Gauge14.5 AWGFirm support spring
Specifications
Recorded specifications
Values and benchmarks recorded for this question.
| Specification | Measured value | Benchmark | Status |
|---|---|---|---|
| 13.75 AWG Spring Constant (k) | 1.65 - 1.85 lbs / inch Deflection Rate | Firm Support Core | pass |
| 14.5 AWG Spring Constant (k) | 1.15 - 1.30 lbs / inch Deflection Rate | Universal Medium-Firm Core | pass |
| 15.0 AWG Spring Constant (k) | 0.75 - 0.90 lbs / inch Deflection Rate | Plush Adaptive Core | pass |
| Tempering Heat Treatment | 450°F Electric Heat-Tempered Carbon Wire | ASTM Spring Wire Standard | pass |
Standards reference: Benchmarks derived from ASTM D3574 (flexible cellular foam), CPSC 16 CFR 1633 (open flame flammability), and clinical capillary closing thresholds (32.0 mmHg).
Checklist
Comparative Spec Verification Checklist
Step-by-step inspection to detect mid-production substitutions and compare component specs.
- 01
Match Gauge to Sleeper Mass
Under 140 lbs: 15.0 AWG; 140-220 lbs: 14.5 AWG; Over 220 lbs: 13.75 AWG.
Watch for: Sleepers over 230 lbs on 15-gauge coils will bottom out into the base foam.
- 02
Inspect Multi-Gauge Zoned Beds
Check if mattress combines 14.5 AWG at head with 13.75 AWG in the center third.
Watch for: Unzoned 15-gauge mattresses allow the heavy pelvis to sink into hammock sag.
- 03
Verify Double-Tempering
Ensure coils are double-tempered to prevent permanent wire deformation over 10 years.
Watch for: Untempered or cheap imported wire takes a permanent sag set within 12 months.
Sources
Sources for this answer
Read the source documents behind the thresholds, measurements, and policy details used here.
View source
Society of Automotive Engineers (SAE)
Mechanical Spring Design and Deflection Fundamentals
SAE Spring Design Manual