General Level I versus Level II: how the sample size changes at AQL 2.5

At the same AQL and the same lot size, general inspection level I gives a code letter equal to or earlier in the alphabet than level II. The table shows what that does to the plan actually used at AQL 2.5. Find your lot size in the first column and compare the two plan columns.

For what the levels are for, see How to choose an inspection level.

Level I and level II side by side at AQL 2.5

Lot size	Code letter, level I	Level I at AQL 2.5	Code letter, level II	Level II at AQL 2.5
2 to 8	A	5 (0/1)	A	5 (0/1)
9 to 15	A	5 (0/1)	B	5 (0/1)
16 to 25	B	5 (0/1)	C	5 (0/1)
26 to 50	C	5 (0/1)	D	5 (0/1)
51 to 90	C	5 (0/1)	E	20 (1/2)
91 to 150	D	5 (0/1)	F	20 (1/2)
151 to 280	E	20 (1/2)	G	32 (2/3)
281 to 500	F	20 (1/2)	H	50 (3/4)
501 to 1,200	G	32 (2/3)	J	80 (5/6)
1,201 to 3,200	H	50 (3/4)	K	125 (7/8)
3,201 to 10,000	J	80 (5/6)	L	200 (10/11)
10,001 to 35,000	K	125 (7/8)	M	315 (14/15)
35,001 to 150,000	L	200 (10/11)	N	500 (21/22)
150,001 to 500,000	M	315 (14/15)	P	500 (21/22)
500,001 and over	N	500 (21/22)	Q	500 (21/22)

Each plan cell reads sample size (Ac/Re). The first number is the sample size. The first bracketed number is Ac: accept the lot if the number of defective units found is Ac or fewer. The second is Re: reject the lot if the number found is Re or more.

If the sample size equals or exceeds the lot size, the table says to do 100 percent inspection. This applies to some of the small-lot cells.

The code letter in each row is the letter for that level. Where the plan shown comes from a different letter, the arrows of the table were followed, as the examples below show.

Where the two levels differ

In the four smallest ranges, from 2 to 8 up to 26 to 50, both levels use the same plan, 5 (0/1).

For 51 to 90 and 91 to 150, level I uses 5 (0/1) and level II uses 20 (1/2).

From 151 to 280 up to 35,001 to 150,000, the level II plan has the larger sample size in every row. Two examples:

• Lot size 151 to 280: level I uses 20 (1/2), level II uses 32 (2/3).
• Lot size 10,001 to 35,000: level I uses 125 (7/8), level II uses 315 (14/15).

For 150,001 to 500,000, level I uses 315 (14/15) and level II uses 500 (21/22).

For 500,001 and over, both levels use 500 (21/22).

Rows where the plan comes from another letter, all of them in the table above:

• Lot size 2 to 8 at level I: code letter A, but the plan used is letter C's, 5 (0/1).
• Lot size 9 to 15 at level I: code letter A, but the plan used is letter C's, 5 (0/1).
• Lot size 16 to 25 at level I: code letter B, but the plan used is letter C's, 5 (0/1).
• Lot size 91 to 150 at level I: code letter D, but the plan used is letter C's, 5 (0/1).
• Lot size 151 to 280 at level I: code letter E, but the plan used is letter F's, 20 (1/2).
• Lot size 2 to 8 at level II: code letter A, but the plan used is letter C's, 5 (0/1).
• Lot size 9 to 15 at level II: code letter B, but the plan used is letter C's, 5 (0/1).
• Lot size 26 to 50 at level II: code letter D, but the plan used is letter C's, 5 (0/1).
• Lot size 51 to 90 at level II: code letter E, but the plan used is letter F's, 20 (1/2).
• Lot size 150,001 to 500,000 at level II: code letter P, but the plan used is letter N's, 500 (21/22).
• Lot size 500,001 and over at level II: code letter Q, but the plan used is letter N's, 500 (21/22).

Where these tables come from

These tables come from MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes (U.S. Department of Defense, 10 May 1989). ANSI/ASQ Z1.4 and ISO 2859-1 descend from it. The tables here were not compared cell by cell with the current paid editions of ANSI/ASQ Z1.4 or ISO 2859-1. Where a contract or purchase order names a standard and an edition, that one governs.

The table covers single sampling plans for normal inspection only.

Questions people ask

What sample size does level I use for a lot of 51 to 90 units at AQL 2.5?

Level I uses code letter C for that range, and the plan is 5 (0/1): a sample of 5, accept on 0 defectives, reject on 1 or more. Level II uses 20 (1/2) for the same lot range.

Which lot sizes get the same plan at both levels?

From 2 to 8 through 26 to 50, both levels use 5 (0/1). From 500,001 and over, both levels use 500 (21/22).

What plan does level II use for 150,001 to 500,000 units?

Level II uses 500 (21/22). Level I uses 315 (14/15) for the same lot range.

Sources

• MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes, U.S. Department of Defense, 10 May 1989: Table I and Table II-A with its legend and footnote. Page scans: archive.org/details/MIL-STD-105E_1. Read 11 October 2026.

Checked 11 October 2026.

This page is an unofficial reference, not affiliated with any standards body, and where your contract names ANSI/ASQ Z1.4, ISO 2859-1 or another standard, use the tables of that edition.