Chip Resistor Rated Power Steps: One Letter Carries Six Different Wattages

We counted 15 chip resistor rated power steps in Walsin’s export and 10 in thin film. The odd ones are not price points — they are footprints. 2/3 W exists only at 1210, 3 W only at 2512, 1/5 W only at 0402, 1.5 W only at 2010.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 203 parametric export files published by Walsin Technology (Walsin) and 28 Walsin datasheets. This post is measured from the 137 chip resistor files totalling 234,815 rows and the 20 thin film files totalling 93,914 rows. Every part number below is real and every count is of part numbers, not pieces.

How many chip resistor rated power steps does Walsin publish?

Fifteen in thick film, ten in thin film, and only nine values appear in both. We parsed all 137 chip resistor exports and all 20 thin film exports. The four largest thick film steps — 1/4 W, 1/8 W, 1/10 W and 1/2 W — carry 137,177 of 234,815 part numbers between them. The five smallest carry 6,792, which is 2.9% of the line.

Rated power	Thick film part numbers	Thin film part numbers	Case sizes it appears at
1/4 W	38,618	8,274	3 thick film, 2 thin film
1/8 W	35,395	8,409	4 thick film, 2 thin film
1/10 W	33,355	12,183	4 thick film, 3 thin film
1.5 W	1,950	0	2010 only
3 W	1,866	0	2512 only
1/5 W	1,665	0	0402 only
1/32 W	1,143	2,556	01005 and the 0201 arrays
2/3 W	168	0	1210 only
2/5 W	0	25,559	1206 and 1210, thin film only

That last row is the one that catches people out. 2/5 W is the single largest rated power step in the whole thin film catalogue — 25,559 of 93,914 part numbers, 27.2% of the line — and it has no thick film counterpart at all. We have not seen this counted anywhere.

Why does each odd power step belong to exactly one case size?

Because each odd step is a named construction, not a rung on a ladder. We grouped all 234,815 thick film rows by rated power and listed the case sizes present at each. Of the 15 steps, five resolve to a single size value, and four of those five are the odd ones. The five odd steps between them occupy five mutually exclusive footprints — no two of them share a case size.

Odd step	Part numbers	Case size	Series it lives in	Match / mismatch against the ordinary step at that size
2/3 W	168	1210	Thick Film Low Ohm Current Sense, commercial and automotive	Mismatch — 1210 otherwise runs 1/2 W, 1/3 W and 3/4 W; 2/3 W sits between two of them
1.5 W	1,950	2010	Thick Film High Power, commercial and automotive	Match on footprint; mismatch — the top rating at 2010, above 1 W
3 W	1,866	2512	High Power, plus metal plate and thick film current sense	Match on footprint; mismatch — the top rating at 2512, above 2 W
1/5 W	1,665	0402	High Power and Triple Power Surge (Automotive)	Match on footprint; mismatch — double the 1/10 W that 0402 usually implies
1/32 W	1,143	01005, 0201×2, 0201×4	General Purpose and the 0201 flat-type arrays	Mismatch — 01005 publishes no other rating, and discrete 0201 is 1/20 W

The contrast is the point. 1 W spans seven case sizes in the thick film export, from 0612 to 2512. 2/3 W spans one. If a selector offers you 2/3 W as a filter, it has already chosen your footprint.

What does the fifth character of the part number actually decide?

The wattage, by way of the case size. We checked all 11,191 rows whose part number carries A in the fifth position. That one letter maps to six different rated powers, and which one you get is decided entirely by the two size digits that sit two characters earlier.

Size code in the part number	Case size	Rated power behind A	Rows measured
04	0402	1/5 W	825
06	0603	1/3 W	1,660
08	0805	1/2 W	1,660
12	1206	3/4 W	1,662
10	1210	3/4 W	1,660
20	2010	1.5 W	1,950
25	2512	3 W	1,774

Three of the five odd steps — 1/5 W, 1.5 W and 3 W — live behind that single letter. WF04A1002FTL, WF20A1002FTL and WF25A1002FZL are all 10 kΩ at ±1% with a temperature coefficient of ≦±100 ppm/°C, all in Thick Film High Power Chip Resistor, and they are rated 1/5 W, 1.5 W and 3 W. The letter is identical. The wattage is not. We have not seen this published anywhere, and it is the cleanest proof we have that an odd power step is a footprint decision wearing a wattage costume.

The companion letter P behaves the same way and lands on the ordinary ladder: 1/8 W at 0402 and 0603, 1/4 W at 0805, 1/2 W at 1206 and 1210, 1 W at 2010, 2 W at 2512. So A is not a different product family. It is the rung above P at whatever size you happened to pick.

Can the same 10 kilohm 0402 be ordered at four different rated powers?

Yes. We filtered the export to 0402, exactly 10,000 Ω, exactly ±1%, and got 25 distinct Walsin part numbers spanning four rated powers — 1/16 W on 17 of them, 1/10 W on three, 1/8 W on three and 1/5 W on two. That is a 3.2 to 1 spread in rated power on one value in one footprint. We will not tell you a part is interchangeable. We will show you where it differs.

Part number	Series	Rated power	TCR	Match / mismatch vs 0402 10 kΩ ±1%
WR04X1002FTL	Thick Film General Purpose	1/16 W	≦±100	Match on size, value, tolerance; the baseline 0402
MR04X1002FTL	Thick Film General Purpose (Automotive)	1/10 W	≦±100	Match on size, value, tolerance; mismatch — 1.6× the rating, automotive series
WF04P1002FTL	Thick Film High Power	1/8 W	≦±100	Match on size, value, tolerance; mismatch — 2× the rating
WF04A1002FTL	Thick Film High Power	1/5 W	≦±100	Match on size, value, tolerance; mismatch — 3.2× the rating
MF04E1002FTL	Thick Film Triple Power Surge (Automotive)	1/5 W	≦±100	Match on size, value, tolerance and rating; mismatch — surge construction, different series
WW04DR005FTL	Metal Foil Low Ohm Power Sensing	1/3 W	≦±100	Mismatch — 0.005 Ω, not 10 kΩ; the only 1/3 W parts at 0402 are five low-ohm sense codes

That last row is worth a second look. 1/3 W at 0402 exists on exactly five part numbers in the whole 234,815-row export, all of them metal foil low-ohm sense parts between 0.005 Ω and 0.025 Ω. A filter that offers “0402, 1/3 W” is offering you a shunt, whether you wanted one or not.

Why is 2/5 W the largest step in thin film and absent from thick film?

Because it belongs to two specific thin film constructions and nothing else. We measured 25,559 rows at 2/5 W across the 20 thin film exports. 20,520 of them are the tantalum nitride MF series at 1206 — and every single one of the 20,520 MF rows in the catalogue publishes 2/5 W and 1206, one rated power and one case size for the entire series. The remaining 5,039 are WF precision at 1210, all of them at ±0.01%.

So “2/5 W” in a thin film line item is not a power budget. It is a declaration that you are on tantalum nitride at 1206, or on the tightest tolerance grade Walsin publishes at 1210. MF12Q10R0ATL is the first — 10.0 Ω, ±0.05%, TCR ≦±50 ppm/°C. WF10F10R0TTL is the second — 10.0 Ω, ±0.01%, TCR ≦±15 ppm/°C. Same rated power. Nothing else in common.

1/32 W splits the same way across the film boundary. In thick film it is 01005 and the 0201 flat-type arrays. In thin film it is discrete 0201 — 2,556 WF rows, and WF02T1000BTL is one of them at 100 Ω, ±0.1%. Discrete 0201 in the thick film export is 1/20 W, not 1/32 W. If a line item reads “0201, 1/32 W”, thick film cannot serve it.

What separates a 2/3 W part from a 3/4 W part at the same value?

Two characters and a space. We read all four rows at 1210 and 0.010 Ω. WW10WR010FTL is 2/3 W. WW10WR010FTL GJ is 3/4 W. Same 1210 footprint, same 0.010 Ω, same ±1%, same temperature coefficient of ≦±600 ppm/°C, same 7″ reel taping — and a 12.5% difference in rated power carried entirely by a suffix with an embedded space in it.

That space is not cosmetic. 39,576 of Walsin’s 234,815 chip resistor part numbers contain an embedded space, which is why these codes fracture when they are pasted into a spreadsheet and sorted. Here the fracture costs you a wattage. A buyer who strips the suffix to make the code paste cleanly has silently downgraded a 3/4 W part to 2/3 W. We have written about that pasting problem before, and this is the sharpest consequence of it we have found.

Do the resistor datasheets we hold cover any of these odd steps?

No — not one of them. We hold 28 Walsin datasheets, 451 pages, and exactly two are chip resistor sheets: Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf and Walsin_WR_General_Purpose_Chip_Resistor.pdf, 20 pages between them. We read both in full. The rated powers they print are 1/4 W, 1/8 W, 1/10 W and 1/16 W on the WR sheet and 1/2 W, 1/4 W, 1/8 W and 1/10 W on the MR sheet. The strings 2/3 W, 1.5 W, 3 W, 1/5 W, 1/32 W and 01005 appear zero times in those 20 pages.

So the five odd steps are the part of Walsin’s chip resistor range for which we hold no derating curve, no maximum working voltage table and no rated-current figure. The WR sheet is ASC_WR_V24, dated September 2016; the MR sheet is ASC_MR_V13, dated March 2024. We tell you what we do not have. Most distributors will not.

The short version

Walsin publishes 15 chip resistor rated power steps and 10 thin film steps, and the odd ones are footprint decisions in disguise. 2/3 W is 1210 and nothing else, 168 part numbers. 1.5 W is 2010, 1,950 part numbers. 3 W is 2512, 1,866. 1/5 W is 0402, 1,665. 1/32 W is 01005 and the 0201 arrays in thick film, discrete 0201 in thin film. 2/5 W is thin film only — 25,559 part numbers, 27.2% of the line, with no thick film counterpart. One letter in the fifth character position carries six different wattages across 11,191 rows, decided by the case size. And a 2/3 W part becomes a 3/4 W part when you add a two-character suffix with a space in it. Qualification stays with you.

Send us the resistor lines off your BOM with the rated power your thermal calculation actually needs and we will come back with Walsin candidates field by field, differences stated, then tell you which of them sat in Hong Kong on 23 September 2026. And if your selector let you tick “2/3 W” without telling you it had just chosen 1210 for you, we would like to know which selector it was.

For the full rating-by-footprint picture, see chip resistor power rating by case size. For why these codes break in a spreadsheet, see why Walsin part numbers do not paste into your BOM. For the surge families behind the 1/5 W step, see anti-surge chip resistors. Cross a whole list in one pass with the free cross-reference tool — paste up to 500 part numbers or drop your Excel or CSV, matched against Walsin’s published catalogue, with every difference from your original stated rather than hidden. Check ready stock before you commit to a production slot; it is a dated snapshot as at 23 September 2026, not a live feed. The full range sits on the Walsin chip resistor page.

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Frequently asked questions

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