Chip Resistor Case Size and Power Rating: 7,480 of 224,672 Walsin Rows Are Out-Rated by a Smaller Case in Their Own Series

Chip resistor case size does not rank power rating. We parsed all 224,672 discrete Walsin rows: 7,480 are rated below a part with a smaller footprint in the same series. The rule “bigger case, more watts” holds in 31 of 38 series and fails in 7, worst in High Power, where 22 percent of rows invert.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds all 137 chip resistor export files published by Walsin Technology (Walsin). This post is written from the Size, Rated Power and Series columns of those files (Thick_Film_High_Power_Chip_Resistor_*.xlsx, Thick_Film_Anti_Surge_Chip_Resistor_*.xlsx and Thick_Film_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx among them), read row by row. We set aside the 10,143 array, network and attenuator rows, whose size field is not a footprint, and measured the other 224,672. Every part number below is real and sits in the export.

Does a larger chip resistor case always carry a higher power rating?

No. In 31 of 38 discrete series it does, and in 7 it does not. We ranked every case size inside each series by nominal footprint, taken from the metric code in the Size column, and counted rows rated below the best rating available at any smaller footprint: 7,480 of 224,672, or 3.3 percent. In the 31 clean series, including every high precision, general purpose, high voltage, trimmable and wide terminal series, the ladder never inverts.

Case size (metric code)	Nominal footprint, mm squared	Series that also list a smaller size	Series where it is out-rated	Match / mismatch against “bigger case, more watts”
0402 (1005)	0.50	7	0	Match in 7 of 7
0603 (1608)	1.28	22	2	Match in 20 of 22; mismatch in High Power and Power Low Ohm
0805 (2012)	2.40	32	3	Match in 29 of 32; mismatch in High Power (both grades) and Anti-Surge
1206 (3216)	5.12	33	0	Match in 33 of 33
1210 (3225)	8.00	17	4	Match in 13 of 17; mismatch in High Power (both grades) and both Power Low Ohm series
2010 (5025)	12.5	21	2	Match in 19 of 21; mismatch in Low Ohm and Metal Plate Power current sense
2512 (6432)	20.5	23	0	Match in 23 of 23

We have not seen this counted anywhere. Nothing in the export flags a part whose rating sits below a smaller neighbour’s, and a filter on case size and a filter on rated power are two separate operations. The footprint figures are nominal products of the two dimensions in the metric code, a convention, not a land-pattern drawing.

Which Walsin series break the case-size rule, and how often?

Seven series, and two of them account for four rows in five. High Power and High Power (Automotive) hold 5,955 of the 7,480 out-rated rows; Anti-Surge and the three current sense series hold the rest. We counted rows, not part-number stems, so a series with more resistance values weighs more. The share is measured against each series’ own rows.

Series (as named in the export)	Rows	Out-rated rows	Share	Larger case, rated lower	Smaller case that out-rates it	Match / mismatch against “bigger case, more watts”
Thick Film High Power Chip Resistor	11,917	2,631	22.1%	0603 1/8 W (831), 0805 1/4 W (831), 1210 1/2 W (969)	0402 1/5 W, 0603 1/3 W, 1206 3/4 W	Mismatch at three sizes
Thick Film High Power Chip Resistor (Automotive)	15,099	3,324	22.0%	0805 1/4 W (1,662), 1210 1/2 W (1,662)	0603 1/3 W, 1206 3/4 W	Mismatch at two sizes
Thick Film Power Low ohm Current Sense Chip Resistor (Automotive)	3,809	575	15.1%	1210 1/2 W (575)	1206 3/4 W	Mismatch at one size
Thick Film Power Low ohm Current Sense Chip Resistor	2,169	326	15.0%	0603 1/10 W (224), 1210 3/4 W (102)	0402 1/8 W, 0815 1 W	Mismatch at two sizes
Thick Film Anti-Surge Chip Resistor	8,340	438	5.3%	0805 1/8 W (435), 0805 1/10 W (3)	0603 1/4 W	Mismatch at one size
Thick Film Low Ohm Current Sense Chip-Resistor	2,622	178	6.8%	2010 1/2 W (178)	1210 2/3 W	Mismatch at one size
Metal Plate Power Low Ohm Current Sense Chip-Resistor	296	8	2.7%	2010 1/2 W (8)	1206 1 W	Mismatch at one size

The other 31 series contribute zero. That includes the entire thin film range, which is a separate export set and is covered in thin film resistor power rating by case size.

What do the out-rated pairs look like part by part?

Like for like on three electrical fields, and still the larger case loses. For 5,159 of the 7,480 out-rated rows we found a smaller-case part in the same series with the same resistance, tolerance and TCR and a higher rated power: 1,973 in High Power, 2,713 in High Power (Automotive), 411 in Anti-Surge and 62 in Power Low Ohm current sense. The remaining 2,321 have no smaller-case twin at identical resistance, tolerance and TCR.

Larger case part	Rated power	Smaller case part	Rated power	Shared fields	Your incumbent part	Match / mismatch
WF08P10R0FTL 0805	1/4 W	WF06A10R0FTL 0603	1/3 W	10.0 ohm, ±1%, ≦±100	___	Match on resistance, tolerance, TCR; mismatch on rated power and footprint
WF10P1R00FTL 1210	1/2 W	WF12A1R00FTL 1206	3/4 W	1.00 ohm, ±1%, ≦±100	___	Match on resistance, tolerance, TCR; mismatch on rated power and footprint
WF06P10R0FTL 0603	1/8 W	WF04A10R0FTL 0402	1/5 W	10.0 ohm, ±1%, ≦±100	___	Match on resistance, tolerance, TCR; mismatch on rated power and footprint
MF08P1R0 JTL 0805	1/4 W	WF06A1R0 JTLJ 0603	1/3 W	1.0 ohm, ±5%, ≦±200	___	Match on resistance, tolerance, TCR; mismatch on rated power, footprint and prefix
WF08S1R0 KTL 0805	1/8 W	WK06S1R0 KTL 0603	1/4 W	1.0 ohm, ±10%, ≦±100	___	Match on resistance, tolerance, TCR; mismatch on rated power, footprint and prefix
WW06ER510FTL 0603	1/10 W	WW04PR510FTL 0402	1/8 W	0.510 ohm, ±1%, ≦±300	___	Match on resistance, tolerance, TCR; mismatch on rated power and footprint

Put your incumbent part number in the blank column and read across. The 0603 part in the first pair carries 1.3 times the rating of the 0805 part while occupying 53 percent of its nominal footprint. We do not state that one is the better choice, because the datasheet we would need is not in our file for these series.

Why does the fifth character of the part number cause the inversion?

Because the fifth character selects a power tier, and tiers are not sorted by case size. In the High Power series the P tier runs 1/8 W at 0402 and 0603, 1/4 W at 0805, 1/2 W at 1206 and 1210, then 1 W and 2 W; the A tier runs 1/5 W, 1/3 W, 1/2 W, 3/4 W, 3/4 W, 1.5 W and 3 W over the same seven sizes. A P part at one size is out-rated by an A part one size down.

The inversion therefore lives between tiers, not inside one. We grouped by series and fifth character together: 1,371 rows still read lower than a smaller footprint, but 933 of those hinge on ten 0402 P rows rated 1/5 W at 1 megohm and above (from HighPower__tol1__ONE_FIFTH_W.xlsx and HighPower__tol5__ONE_FIFTH_W.xlsx) and on four rows at the odd 0815 size, not on the main ladder. The other 438 are Anti-Surge, below. The fifth-character mechanism itself is described in one letter, six wattages, already published. What is new here is the count of rows that cross it the wrong way.

Four rows at 0815 deserve a mention of their own: they are the only 0815 parts in the catalogue, rated 1 W, and they make the 102 Power Low Ohm 1210 rows at 3/4 W appear out-rated. We left them in the count and show them in the series table.

Does the inversion ever happen inside a single type code?

Yes, once cleanly, in Anti-Surge. That series has a single type code, S, and its ladder still inverts. At 0603 the S code is rated 1/10 W on 432 rows and 1/4 W on 435; at 0805 it is rated 1/10 W on 3 rows, 1/8 W on 435 and 1/4 W on 1,146; the 438 lowest-rated 0805 rows are therefore out-rated by 0603.

This matters because 1/8 W exists in Anti-Surge at 0805 only. A buyer who filters on 1/8 W lands on 0805 and may infer that 0805 is the lower rung of a continuous ladder. It is not: the 0603 shelf reaches 1/4 W. Wattage gaps in this series are examined cell by cell in anti-surge wattage gaps.

How should a design select by wattage when the ladder inverts?

Filter on the number first and the footprint second. Convert the Rated Power strings to watts, sort the candidate rows by rated power, and only then read the case size; 7,480 of 224,672 rows would be missed or mis-ranked by a sort on size alone. The string itself mixes fractions and decimals (1/8W, 1.5W), so sort the numeric value, not the text.

Three working rules follow from the counts above:

1. Read the fifth character with the case size. P and A in the High Power series are different tiers; 0805P is not “the 0805 rating”.
2. Check the footprint you are leaving. If a smaller case at the same value carries the higher rating, the larger case buys board area, not watts.
3. Confirm the rating against the document. We hold 28 Walsin datasheets, 451 pages, and two are chip resistor sheets, WR general purpose and MR automotive. We hold none for the High Power, Anti-Surge or current sense series, so every rating above is the export’s figure and should be confirmed with Walsin before you qualify.

The free cross-reference tool lists differences from your original part field by field, rated power included. What sits in Hong Kong is on ready stock: 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed. The wider range sits on the chip resistor page, and the case-size basics are in chip resistor power rating by case size.

The short version

Chip resistor case size is not a power ladder across tiers. We parsed 224,672 discrete Walsin rows in 38 series: 31 series never invert, 7 do, and 7,480 rows (3.3 percent) are rated below a smaller footprint in their own series. High Power and its automotive twin hold 5,955 of them. 5,159 have a like-for-like smaller part, for example WF06A10R0FTL at 1/3 W against WF08P10R0FTL at 1/4 W. The cause is the fifth character, which picks a power tier. Anti-Surge inverts inside one code. We will not tell you which part to fit. We will show you the rating the file holds. Qualification stays with you.

Send us the resistor lines on your BOM with the rated power your thermal calculation needs, and we will list every Walsin row at or above it, smallest footprint first. And a question back: when you last moved up a case size for more watts, did you read the rating of the part you left?

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Frequently asked questions

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