Brinell Hardness Calculator and Conversion Table (ASTM E140)

A brinell hardness calculator saves you from transcription errors when speccing mold steel, and errors here cost real money. A cavity block ordered at 28 HRC instead of 38 HRC can fail in fewer than 50,000 shots on a glass-filled nylon tool. This reference gives you the full Brinell to Rockwell conversion table per ASTM E140, plus hardness specs for the four mold steels we specify most often.

What ASTM E140 Actually Governs

ASTM E140 is the standard hardness conversion table for metals, published by ASTM International and last revised in 2023. It does not define a test method. It converts values across scales: Brinell (HBW), Rockwell (HRC, HRB), Vickers (HV), and Knoop (HK). The standard covers ferrous metals separately from non-ferrous, and mold steels fall under the hardened steel tables in Annex A1.

The Brinell test uses a 10 mm tungsten carbide ball indenter under a 3,000 kgf load for steels above 100 HBW. The resulting indentation diameter is measured optically and converted to a hardness number. Brinell readings above 650 HBW are unreliable because the ball itself deforms, which is why fully hardened H13 at 48 to 52 HRC is typically reported in Rockwell, not Brinell.

Conversions in ASTM E140 carry a stated uncertainty. The standard notes that converted values are approximations and should not be used in place of directly measured values for contractual acceptance. When your supplier sends a material cert with a Brinell number and you need an HRC equivalent for your drawing callout, use the table below as a working reference, then verify with a direct Rockwell test on the actual block.

Full Brinell to Rockwell Conversion Table (ASTM E140, Hardened Steel)

The table below covers the range most relevant to mold steel procurement: 150 HBW through 650 HBW. Vickers values and approximate tensile strength in ksi are included. Tensile strength correlation is from ASTM E140 Annex A1 and applies to carbon and alloy steels only. Do not apply these tensile figures to stainless or tool steels without separate verification.

Brinell (HBW)	Rockwell C (HRC)	Rockwell B (HRB)	Vickers (HV)	Tensile Strength (ksi)
150	not applicable	79.6	157	75
163	not applicable	83.9	171	82
179	not applicable	87.1	188	90
197	not applicable	90.2	207	99
217	19.0	95.0	228	109
229	21.3	96.7	240	115
241	23.1	98.1	253	121
255	25.2	99.8	268	128
269	27.1	not applicable	282	135
285	29.2	not applicable	299	143
302	31.3	not applicable	317	152
321	33.4	not applicable	337	162
341	35.5	not applicable	358	172
363	37.7	not applicable	381	183
388	40.0	not applicable	407	196
415	42.4	not applicable	436	210
444	44.9	not applicable	466	224
477	47.5	not applicable	500	241
514	50.3	not applicable	539	260
555	53.3	not applicable	583	281
601	56.5	not applicable	630	not applicable
650	59.9	not applicable	682	not applicable

HRB scale tops out at 100 and becomes unreliable above roughly 240 HBW. Values below 20 HRC are better expressed in HRB or HBW. ASTM E140 Table 1 is the authoritative source; the values above are extracted from that table and rounded to one decimal for HRC.

Mold Steel Hardness Specs: P20, H13, S7, and 420SS

These four grades cover the large majority of offshore cavity, core, and structural components we specify. Mold steel hardness tolerances on your drawing directly control what heat treatment your Chinese supplier performs, and a vague callout like “hardened” is a defect waiting to happen.

Steel Grade	Typical Use	Target HRC	Equivalent HBW (approx.)	Notes
P20	Core, cavity, large frames	28 to 34	270 to 320	Pre-hardened, no further HT required. Good for runs under 500,000 shots with unfilled resins.
H13	Cavity inserts, cores, hot runner gates	48 to 52	approx. 480 to 525	Through-hardened and tempered. Required for glass-filled, mineral-filled, and high-temperature resins. Confirm with direct HRC test per ASTM E18.
S7	Side actions, cams, high-impact components	54 to 56	approx. 555 to 580	Superior toughness versus D2. Use where side-action impact loads are high.
420SS	Cavity inserts for PVC, corrosive resins	48 to 52	approx. 480 to 525	Hardness achievable only with proper austenitizing at 1850 to 1950 degrees F. Verify chemistry before ordering.

P20 is delivered pre-hardened at 28 to 34 HRC, which converts to roughly 271 to 321 HBW on the brinell calculator table above. That range is why you will see Brinell certs on incoming P20 bar stock: the Brinell test is easier to run on large blocks than Rockwell, which requires a flat, polished surface. Once the block is machined and the mold is built, Rockwell is the practical test.

H13 at 48 to 52 HRC is the workhorse for filled resins. At 30% short glass fill in nylon 66, cavity surface pressures can exceed 15,000 psi. A cavity running at 40 HRC instead of 50 HRC will show measurable wear before 200,000 shots. The cost difference between a cavity rework and getting the hardness right at source is real: we have seen cavity re-steel costs run $8,000 to $22,000 depending on complexity, versus a $200 hardness audit at incoming inspection.

How to Use a Brinell Calculator: Worked Example

Your supplier sends a material cert for a P20 cavity block. The cert shows 295 HBW. Your drawing callout is 28 to 34 HRC. Is the block in spec?

Step 1: Find 285 HBW and 302 HBW in the table above. At 285 HBW the converted value is 29.2 HRC. At 302 HBW the converted value is 31.3 HRC. Interpolating linearly, 295 HBW sits at approximately 30.4 HRC.

Step 2: Compare to your callout. 30.4 HRC falls inside 28 to 34 HRC. The block passes on conversion. But per ASTM E140, converted values are approximations. For a contractual decision, you should follow up with a direct Rockwell C test on a ground surface of the block.

Step 3: If the block read 265 HBW on the cert, the conversion gives approximately 26.7 HRC. That is below your 28 HRC floor. Reject the cert and request either a re-test or a new block. Do not accept a waiver without understanding what caused the low reading, whether it is a chemistry issue or an incomplete temper cycle.

Our project managers use this exact workflow on every incoming material cert review. A brinell calculator that automates the interpolation step reduces review time from about 8 minutes per cert to under 60 seconds when you are processing a multi-cavity tool with 12 to 16 component certs.

Reading the Brinell to Rockwell Conversion Across the Full Range

The brinell to rockwell conversion is not linear. The relationship steepens as you move up the scale. Between 217 HBW and 285 HBW, each 10 HBW increment corresponds to roughly 1.2 HRC. Between 477 HBW and 555 HBW, that same 10 HBW increment is closer to 1.9 HRC. This non-linearity is why linear interpolation between distant table entries introduces error, and why ASTM E140 recommends using the nearest tabulated value.

The Vickers scale tracks closely with Brinell at lower hardness levels. Above 400 HBW the two diverge by up to 5 percent. For precision surface treatments like PVD coatings on cavity faces, Vickers (HV) is the preferred test because the indenter is smaller and you can test closer to the coated surface. A TiN coating typically reads 2,200 to 2,400 HV on a microhardness tester, which is well outside the range of the macro-Brinell test.

Frequently Asked Questions

What is the difference between HBW and HBS in the Brinell test?

HBS used a hardened steel ball indenter and is now obsolete. HBW uses a tungsten carbide ball, which is harder and does not deform at high loads. ASTM E10, the Brinell test method standard, specifies HBW only. Any modern material cert should show HBW. If you see HBS on a cert from a supplier, ask when the test equipment was last calibrated.

Can I use this brinell calculator table for aluminum mold components?

No. ASTM E140 provides separate tables for non-ferrous metals including aluminum alloys. The ferrous table above applies to carbon, alloy, and tool steels only. For 7075-T6 aluminum (used in prototype and low-volume tooling), the relevant range is 87 to 91 HRB, and the Brinell equivalent runs approximately 175 to 185 HBW on the non-ferrous table.

How accurate is the brinell to rockwell conversion from a cert alone?

ASTM E140 states that converted hardness values are approximations and should not substitute for direct measurement in acceptance testing. The conversion uncertainty is typically plus or minus 2 HRC in the 20 to 45 HRC range. For critical cavity components, use the converted value as a screening check and follow up with a direct HRC test per ASTM E18 before final acceptance.

What hardness should I specify for a P20 mold running 10 million shots?

P20 is not the right choice at 10 million shots with any abrasive or filled resin. At that volume with unfilled resins and a polished cosmetic requirement, you should upgrade to H13 at 48 to 52 HRC. At 10 million shots with 30 percent glass fill, consider 420SS or a premium tool steel like Bohler M390, which runs 58 to 62 HRC. The steel upgrade cost on a four-cavity tool is typically $3,000 to $7,000, versus a cavity replacement cost that can exceed $30,000.

Does mold steel hardness affect cycle time?

Hardness itself does not change thermal conductivity enough to affect cycle time in most cases. What does affect cycle time is the cooling line design and steel grade. Beryllium copper inserts in high-heat areas run thermal conductivity of roughly 105 BTU per hour per foot per degree F versus 20 BTU for P20. That difference can cut local cycle time by 15 to 25 percent in deep-rib geometry. Specify hardness for wear life; specify steel grade and insert material for thermal performance.

Use our free hardness converter tool at /tools/hardness-converter to run interpolated ASTM E140 conversions across HBW, HRC, HRB, and HV without manual table lookups. If you need a full incoming inspection protocol for offshore tooling, our injection molding consulting team covers hardness verification as part of the standard pre-shipment audit at /services/tooling-audit.