A DIP-28 is either 7.62 mm or 15.24 mm between lead rows, and the narrow one is the package almost everyone means. Pitch stays 2.54 mm in both. The term SPDIP causes most of the confusion here, and it does not mean what the name suggests. This page gives the verified dimensions, the pin-1 rule and the hole-size arithmetic.

Key takeaways

• Pitch is 2.54 mm (0.100 in) on every mainstream DIP-28. Row spacing is 7.62 mm (300 mil) or 15.24 mm (600 mil).
• The 300-mil part dominates. The ATmega328P-PU alone shows 53,703 units in stock at DigiKey.
• SPDIP on a 28-pin microcontroller means Skinny DIP at 2.54 mm pitch, not Shrink DIP at 1.778 mm pitch. The two share an abbreviation and are not interchangeable.
• A 28-pin body is long: Microchip lists the PIC16F882-I/SP at 34.67 mm, roughly 1.37 in.
• The hole pattern spans 33.02 mm end to end in both widths, since 13 spaces × 2.54 mm is fixed by pin count.
• Memory parts skew 600 mil; microcontrollers skew 300 mil. Check the distributor package field before laying out.

What is a DIP-28 package?

A DIP-28 package is a 28-lead dual in-line package: a rectangular molded body with fourteen through-hole leads down each long side on 2.54 mm pitch. The two lead rows sit either 7.62 mm or 15.24 mm apart. It mounts through plated holes or into an IC socket. PDIP-28 denotes the plastic-bodied version.

This is the most searched DIP size, and the reason is the ATmega328P. Atmel defines its package 28P3 as a 28-lead, 0.300 in wide plastic dual inline package, which is the part sitting in every socketed Arduino Uno. Most DIP-28 traffic is someone building around that chip or one of its PIC equivalents.

Distributors disambiguate the width in the package field. DigiKey lists the ATMEGA328P-PU as 28-DIP (0.300″, 7.62mm) with supplier device package 28-PDIP. A listing that gives only “28-PDIP” or “DIP-28” is not enough to lay out from.

[IMAGE 1: DIP-28 package outline drawing with body length, row spacing, pitch and lead dimensions, showing 300-mil and 600-mil variants side by side | alt: “DIP-28 package dimensions diagram showing 2.54 mm pitch with 7.62 mm and 15.24 mm row spacing”]

SPDIP: the abbreviation that causes wrong footprints

This deserves its own section because it produces real board respins. SPDIP is used for two different things.

• Shrink Plastic DIP means a reduced lead pitch of 1.778 mm (0.070 in). Mill-Max sells header and socket series built specifically for this pitch. It is a genuinely different grid.
• Skinny DIP means a normal 2.54 mm pitch package in a narrow 300 mil body, used to distinguish it from the 600 mil version at the same pin count.

On 28-pin microcontrollers, SPDIP nearly always means the second one. Microchip lists the PIC16F882-I/SP with package type SPDIP and a body 34.67 mm long by 7.62 mm wide. A 28-pin part at 1.778 mm pitch would be roughly 24 mm long, not 34.67 mm. The arithmetic settles it: 13 spaces at 1.778 mm is 23.1 mm, while 13 spaces at 2.54 mm is 33.02 mm, which fits a 34.67 mm body.

Microchip reinforces this in its own packaging specification, which lists a 28-Lead Skinny Plastic Dual In-Line (SPDIP) at 300 mil body and a separate 28-Lead Plastic Dual In-Line (PDIP) at 600 mil body. Both are 2.54 mm pitch parts. Neither is a shrink-pitch package.

The practical rule: if the part is a 28-pin microcontroller marked SPDIP, use the 2.54 mm pitch footprint. Only treat SPDIP as 1.778 mm pitch when the datasheet drawing explicitly gives that pitch, which is mostly older memory and video controller parts.

DIP-28 dimensions

Published dimensions for the 300-mil 28-pin package, from manufacturer and distributor parametric data:

Dimension	Value	Source
Lead pitch	2.54 mm (0.100 in)	Atmel 28P3 / Microchip SPDIP
Row spacing, nominal	7.62 mm (0.300 in)	DigiKey package field, ATMEGA328P-PU
Body length (PIC16F882-I/SP)	34.67 mm	Microchip parametric data
Body width (PIC16F882-I/SP)	7.62 mm	Microchip parametric data
Body height (PIC16F882-I/SP)	3.43 mm	Microchip parametric data
Hole pattern length	33.02 mm	Calculated: 13 × 2.54 mm
Socket outline, 0.3 in 28-pin	35.6 × 10.07 × 4.75 mm	Addicore DIP-28 socket, pins excluded

Two figures are worth separating. The hole pattern length of 33.02 mm is fixed by pin count and pitch, so it is identical for every DIP-28 regardless of width or vendor. Body length is not fixed and varies by manufacturer, which is why the PIC figure above is attributed to a specific part rather than presented as a universal value.

Socket outlines run longer than the IC. The Addicore 0.3 in 28-pin socket measures 35.6 mm long excluding pins, about 1 mm more than the PIC body. Allow for that in keepout if the design is socketed.

Why a DIP-28 is physically awkward

At 33.02 mm of hole pattern, a DIP-28 is over 1.3 in long. Two consequences follow.

First, board area. A 300-mil DIP-28 occupies roughly 33 by 8 mm of hole grid before clearance. The SOIC-28 equivalent is a fraction of that, which is the honest argument against DIP for anything past prototype quantities.

Second, insertion force. Twenty-eight leads is enough that hand insertion into a fresh socket needs real pressure, and the leads splay outward from the factory. Most people roll the package against a flat surface to bring both rows to vertical before inserting. Use an IC extractor rather than a screwdriver on removal, because prying at one end bends the far-row leads.

DIP-28 pinout and pin 1 identification

Pin 1 sits at one end, marked by a notch, a molded dot, or a chamfered corner. Orient the package with the notch at the top and the leads pointing away from you. Pin 1 is the upper-left lead. Numbering runs down the left side to pin 14, across the end, and back up the right side from pin 15 to pin 28.

For a DIP-28 specifically:

• Left column, top to bottom: pins 1 through 14
• Right column, bottom to top: pins 15 through 28
• Pin 1 and pin 28 face each other across the body
• Pin 14 and pin 15 face each other at the opposite end

The ATmega328P datasheet pin-out is a useful reference for the convention: PC6/RESET is pin 1 at the notch end, PD0 through PD4 run down the left side, VCC is pin 7 and GND pin 8, and the count returns up the right side to PC5 at pin 28.

One trap specific to this device family. The 28-pin DIP and the 32-pin TQFP versions of the ATmega328P do not share a pin map, and the TQFP adds ADC6 and ADC7 which do not exist on the DIP. Porting a design between the two packages is a schematic change, not a footprint swap.

[IMAGE 2: Top-down DIP-28 pinout diagram with notch, pin 1 dot, and numbering 1 to 28 counterclockwise | alt: “DIP-28 pinout diagram showing pin 1 notch and counterclockwise pin numbering to pin 28”]

DIP-28 footprint: hole and pad sizing

Fourteen holes per row on 2.54 mm pitch, rows at either 7.62 mm or 15.24 mm. The hole pattern spans 13 × 2.54 mm = 33.02 mm end to end in both widths.

Size the hole from the maximum lead width in your specific datasheet. Typical 300-mil plastic DIP lead width maxima fall around 0.51 to 0.57 mm; the worked example below uses 0.57 mm as a conservative case. Always confirm against the drawing for the part you are actually placing.

Applying the IPC-2222 density levels to a 0.57 mm maximum lead:

• Level A: minimum hole = max lead diameter + 0.25 mm → 0.57 + 0.25 = 0.82 mm
• Level B: + 0.20 mm → 0.77 mm
• Level C: + 0.15 mm → 0.72 mm

Then the pad. Pad diameter = minimum hole size + (2 × minimum annular ring) + minimum fabrication allowance, where the minimum annular ring is 0.05 mm and the fabrication allowance is 0.6 mm for Level A, 0.5 mm for Level B and 0.4 mm for Level C.

Level B worked through: 0.77 + (2 × 0.05) + 0.5 = 1.37 mm pad on a 0.77 mm hole.

Round the hole up to a stocked drill. 0.8 mm is standard and clears a 0.57 mm lead comfortably. A 1.5 mm pad on a 0.8 mm hole is a manufacturable Class 2 default for a general-purpose DIP-28.

Two checks before committing:

• Aspect ratio. Keep board thickness to hole diameter under 10:1 for reliable plating. A 0.8 mm hole is good to 8 mm of board, so this never binds on a 1.6 mm stackup.
• Annular ring class. IPC-6012 Class 3 requires a minimum 0.001969 in external-layer annular ring measured from the finished hole to the land edge. Class 2 permits 90-degree breakout provided the land-conductor junction is teardropped. Class 3 means adding pad, not shaving hole.

Routing under a 300-mil DIP-28

The 7.62 mm row spacing leaves a usable channel between the two hole rows. With 1.5 mm pads on 7.62 mm centres, the clear gap between opposing pad edges is about 6.1 mm, which accommodates several routed traces on a two-layer board.

That channel is where the decoupling capacitor should go. For the ATmega328P, place a 100 nF ceramic as close as possible to the VCC and GND pins, pins 7 and 8 on the DIP. Running the decoupling on the far side of the package wastes the advantage the channel gives you.

Library footprints

The KiCad Package_DIP library carries DIP-28 at two through-hole row spacings, plus SMD socket and surface-mount DIP variants:

• DIP-28_W7.62mm — 300 mil, plus LongPads, Socket and Socket_LongPads variants
• DIP-28_W15.24mm — 600 mil, plus LongPads, Socket and Socket_LongPads variants
• DIP-28_W8.89mm and DIP-28_W16.51mm — SMD socket variants at 350 and 650 mil
• SMDIP-28_W15.24mm — surface-mount DIP at 600 mil

Unlike DIP-24, there is no 400-mil DIP-28 in the stock library, so the choice is a clean two-way one. Type the width rather than picking from an autocomplete list.

300 mil against 600 mil: which DIP-28 do you have?

	300 mil (7.62 mm)	600 mil (15.24 mm)
Row spacing	7.62 mm	15.24 mm
Hole pattern length	33.02 mm	33.02 mm
Typical devices	Microcontrollers (ATmega, PIC)	Parallel EEPROM, SRAM, EPROM
Common vendor label	SPDIP or 28-PDIP	28-PDIP
KiCad stock footprint	Yes	Yes
Breadboard	Straddles the centre channel	Too wide for a standard breadboard

The device-type split is a reliable heuristic at 28 pins. Microcontrollers went narrow because they had to fit prototyping boards. Parallel memory stayed wide because the die and the lead frame needed the room. If you are looking at an EEPROM or SRAM, expect 600 mil until proven otherwise.

Measuring settles it in one pass. Span the outside of the lead rows with calipers. A 300-mil DIP-28 reads under 9 mm across the lead tips. A 600-mil part reads over 15 mm. There is no overlap.

Availability and cost

Unlike 24-pin DIP logic, the 28-pin DIP is in robust health, carried by the microcontroller demand. Verified DigiKey listings:

Part	Function	Package	Status	Qty-1	Stock
ATMEGA328P-PU	AVR MCU, 32 KB flash	28-DIP (0.300 in)	Active	$2.89	53,703
ATMEGA328-PU	AVR MCU, non-P variant	28-DIP (0.300 in)	Active	$2.63	13,645
PIC16F886-I/SP	PIC MCU, 14 KB flash	28-SPDIP (0.300 in)	Active	—	—
AT28C256-15PU	Parallel EEPROM, 256 Kbit	28-DIP	Active	$9.34	—
AT28C64B-15PU	Parallel EEPROM, 64 Kbit	28-DIP	Active	$5.50	—

Two observations. The ATmega328P-PU at 53,703 units in stock is not a part anyone needs to second-source under pressure, which is unusual for a through-hole device in 2026. Its cost curve is shallow, dropping from $2.89 at quantity 1 to $2.39 at 100, so there is little volume advantage to be had.

Parallel memory in DIP-28 costs several times more than the microcontrollers. The AT28C256-15PU at $9.34 reflects low-volume legacy production rather than any technical premium. If a design needs bulk parallel EEPROM, the DIP package is the expensive way to buy it.

For designs that must stay through-hole after a part goes end of life, a SOIC-28 to DIP-28 adapter converts a surface-mount device to a 0.6 in DIP footprint on 2.54 mm centres. That keeps socketed and repairable equipment viable.

[IMAGE 3: A 300-mil DIP-28 microcontroller beside a 600-mil DIP-28 memory IC and a 28-pin socket | alt: “DIP-28 package in 300 mil and 600 mil widths next to a 28-pin IC socket”]

Design mistakes that cause rework

• Reading SPDIP as 1.778 mm pitch. On 28-pin microcontrollers it means Skinny DIP at 2.54 mm pitch. Check the drawing pitch, not the abbreviation.
• Picking the footprint by pin count alone. DIP-28 exists at 300 and 600 mil. Type the width explicitly.
• Silkscreen drawn to the hole pattern. The pattern is 33.02 mm but bodies run longer, around 34.67 mm on the PIC16F882. Sockets are longer still at about 35.6 mm.
• Hole sized from nominal lead width. Size from the datasheet maximum, then round up to a stocked drill.
• Decoupling placed outside the row channel. The 6 mm gap between pad rows exists so the bypass cap can sit next to the supply pins. Use it.
• Assuming DIP and TQFP pin maps match. On the ATmega328P they do not, and the TQFP carries two ADC channels the DIP lacks.

Frequently asked questions

What is a DIP-28 package?

A 28-lead dual in-line package with fourteen through-hole leads per side on 2.54 mm pitch. Row spacing is 7.62 mm or 15.24 mm, with the narrow version far more common. The plastic version is called PDIP-28. It mounts through plated holes or into an IC socket.

What are the dimensions of a DIP-28?

Pitch is 2.54 mm and the hole pattern spans 33.02 mm end to end in both widths. Body length varies by vendor; Microchip lists the PIC16F882-I/SP at 34.67 mm long, 7.62 mm wide and 3.43 mm high. Check your specific datasheet for exact limits.

Is SPDIP the same as DIP-28?

Usually yes on microcontrollers. SPDIP there means Skinny DIP, a 300 mil wide body at normal 2.54 mm pitch. SPDIP can also mean Shrink DIP at 1.778 mm pitch on some older memory parts, which is a different grid. Confirm the pitch on the drawing.

How do I identify pin 1 on a DIP-28?

Look for a notch, molded dot, or chamfer at one end. With the notch at the top and leads pointing away, pin 1 is the upper-left lead. Numbering runs counterclockwise: down the left to pin 14, then up the right side from 15 to 28.

What hole size should I use for a DIP-28 footprint?

Size from the maximum lead width in your datasheet. For a 0.57 mm maximum, IPC-2222 Level B gives 0.77 mm minimum and Level A gives 0.82 mm. Round to a standard 0.8 mm drill with a 1.5 mm pad for a Class 2 default.

Is the ATmega328P a 300 mil or 600 mil DIP-28?

It is 300 mil. Atmel defines its package 28P3 as a 28-lead, 0.300 in wide plastic dual inline package, and DigiKey lists the ATMEGA328P-PU as 28-DIP (0.300 in, 7.62 mm). It fits a standard breadboard, straddling the centre channel.

What to do next

Settle two things before placing anything. First, the row spacing: read it off the distributor package field or measure across the lead tips. Second, if the part is labelled SPDIP, confirm the pitch on the datasheet drawing rather than assuming from the abbreviation. Those two checks prevent every expensive DIP-28 mistake.

With both known, use the matching stock library footprint. Cut a custom one only for IPC Class 3 annular ring margin, or when socketing and you want the socket-specific pad geometry.

If the design is a new build rather than a repair or a teaching board, price the SOIC-28 version before committing to through-hole. The DIP is worth its board area when the part needs to be swapped, socketed or hand-assembled. Outside those cases, the surface-mount part is smaller and usually cheaper.