Arduino Uno vs Mega 2560
Both are 5 V, 16 MHz AVR boards, but the Mega 2560 has 54 digital pins (15 PWM), 16 analog inputs, four hardware serial ports, 256 KB of flash and 8 KB of SRAM, against the Uno's 14 digital pins, 6 analog inputs, one serial port, 32 KB and 2 KB (Arduino Mega 2560 Rev3 datasheet, pp. 1, 2; Arduino UNO R3 tech specs). Choose the Mega when you run out of pins, serial ports or memory, as in 3D printers, robots and large LED or sensor arrays; otherwise the smaller Uno does the job.
Side by side
| Arduino Uno | Mega 2560 | |
|---|---|---|
| MicrocontrollerArduino UNO R3 tech specs; Arduino Mega 2560 Rev3 datasheet (A000067), p. 1 | ATmega328P, 16 MHz, 5 V | ATmega2560, 16 MHz, 5 V |
| MemoryArduino UNO R3 tech specs; Mega 2560 Rev3 datasheet, p. 2 | 32 KB flash, 2 KB SRAM, 1 KB EEPROM | 256 KB flash (8 KB bootloader), 8 KB SRAM, 4 KB EEPROM |
| Digital I/OArduino UNO R3 tech specs; Mega 2560 Rev3 datasheet, p. 2 | 14 (6 PWM) | 54 (15 PWM: D2 to D13, D44 to D46) |
| Analog inputsArduino UNO R3 tech specs; ATmega328P datasheet, p. 2; Mega 2560 Rev3 datasheet, p. 2 | 6, 10-bit | 16, 10-bit |
| Hardware serial portsArduino UNO R3 datasheet, p. 10; Arduino Mega 2560 Rev3 store description | 1 (D0/D1) | 4 (D0/D1, D19/D18, D17/D16, D15/D14) |
| I2C pinsArduino UNO R3 datasheet, p. 10; Mega 2560 Rev3 datasheet, p. 10 | A4 (SDA), A5 (SCL) | D20 (SDA), D21 (SCL) |
| SPI pinsArduino UNO R3 datasheet, p. 10; Mega 2560 Rev3 store description | D10 (SS), D11 (MOSI), D12 (MISO), D13 (SCK) | D53 (SS), D51 (MOSI), D50 (MISO), D52 (SCK) |
| Input voltage (VIN / jack)Arduino UNO R3 tech specs; Mega 2560 Rev3 datasheet, p. 5 | 7 to 12 V recommended, 6 to 20 V limit | 7 to 12 V recommended, 6 to 20 V limit |
| Size and weightArduino UNO R3 tech specs; Mega 2560 Rev3 tech specs | 68.6 × 53.4 mm, 25 g | 101.52 × 53.3 mm, 37 g |
Which one to pick
- Most projects: a handful of sensors, LEDs, a display and a motor driver fit in 14 digital pins and 6 analog inputs (Arduino UNO R3 tech specs).
- Compact builds: the Uno is 68.6 × 53.4 mm against the Mega's 101.52 × 53.3 mm.
- Following tutorials and shields written for the Uno's pin map, I2C on A4/A5 and SPI on D10 to D13.
- Pin-hungry builds: 3D printers and CNC controllers, robots with many servos, large keypads and LED arrays (54 digital pins, Mega 2560 Rev3 datasheet, p. 2).
- Several serial devices at once, such as a GPS, a Bluetooth module and a fingerprint reader, each on its own hardware UART.
- Sketches that run out of the Uno's 32 KB flash or 2 KB SRAM: the Mega has 256 KB and 8 KB (datasheet, p. 2).
Swapping one for the other
What changes in the wiring and the code.
- Both run 5 V logic at 16 MHz, so sensors and modules keep their wiring voltage and most sketches compile unchanged once you select Arduino Mega or Mega 2560 in the IDE.
- Move I2C from A4/A5 to D20 (SDA) and D21 (SCL) (Mega 2560 Rev3 datasheet, p. 10); the SDA and SCL pins beside AREF carry the same bus on both boards.
- Move SPI from D10 to D13 to D50 (MISO), D51 (MOSI), D52 (SCK) and D53 (SS), or take it from the 6-pin ICSP header, which carries SPI on both boards. Shields that hard-wire SPI to D11 to D13 need the ICSP pins on the Mega.
- A module on SoftwareSerial, or sharing D0/D1 with USB, can move to Serial1, Serial2 or Serial3 on the Mega. External interrupts are on D2, D3, D18, D19, D20 and D21 (Mega store description).
Arduino Uno or Mega 2560: questions
Do Uno shields work on the Arduino Mega?
Most do: the Mega shares the Uno's header layout at the shield end. Shields that use I2C on A4/A5 or SPI on D11 to D13 expect the Uno's pinout; on the Mega, I2C is D20/D21 and SPI is D50 to D53 (Mega 2560 Rev3 datasheet, p. 10), so those shields need the SDA/SCL pins or the ICSP header.
Is the Mega faster than the Uno?
No. Both run an 8-bit AVR at 16 MHz (UNO R3 tech specs; Mega 2560 Rev3 datasheet, p. 1). The Mega has more pins, serial ports and memory, not more speed.
How many serial ports does each board have?
The Uno has one hardware UART on D0/D1, shared with USB (UNO R3 datasheet, p. 10). The Mega has four: Serial on D0/D1, Serial1 on D19/D18, Serial2 on D17/D16 and Serial3 on D15/D14 (Mega 2560 Rev3 store description).
Why doesn't my I2C sensor answer on the Mega?
It is probably still on A4 and A5. On the Mega, SDA is D20 and SCL is D21 (Mega 2560 Rev3 datasheet, p. 10), also repeated on the two pins beside AREF.
How much current can each pin supply?
The same on both: 20 mA recommended per I/O pin, 40 mA absolute maximum (Arduino tech specs; ATmega328P datasheet, p. 308; ATmega2560 datasheet 2549Q, p. 355). The 3.3V pin gives 50 mA on both boards.
The two references
Checked on 2026-10-29 against 4 sources, the makers’ datasheets first.
This comparison as plain Markdown. /compare/arduino-uno-vs-arduino-mega.md