Build MMCV from source

Build on Linux or macOS

After cloning the repo with

git clone
cd mmcv

You can either

  • install the lite version

    pip install -e .
  • install the full version

    MMCV_WITH_OPS=1 pip install -e .

If you are on macOS, add the following environment variables before the installing command.

CC=clang CXX=clang++ CFLAGS='-stdlib=libc++'


CC=clang CXX=clang++ CFLAGS='-stdlib=libc++' MMCV_WITH_OPS=1 pip install -e .


If you would like to use opencv-python-headless instead of opencv-python, e.g., in a minimum container environment or servers without GUI, you can first install it before installing MMCV to skip the installation of opencv-python.

Build on Windows

Building MMCV on Windows is a bit more complicated than that on Linux. The following instructions show how to get this accomplished.


The following software is required for building MMCV on windows. Install them first.

  • Git

    • During installation, tick add git to Path.

  • Visual Studio Community 2019

    • A compiler for C++ and CUDA codes.

  • Miniconda

    • Official distributions of Python should work too.

  • CUDA 10.2

    • Not required for building CPU version.

    • Customize the installation if necessary. As a recommendation, skip the driver installation if a newer version is already installed.

You should know how to set up environment variables, especially Path, on Windows. The following instruction relies heavily on this skill.

Setup Python Environment

  1. Launch Anaconda prompt from Windows Start menu

    Do not use raw cmd.exe s instruction is based on PowerShell syntax.

  2. Create a new conda environment

    conda create --name mmcv python=3.7  # 3.6, 3.7, 3.8 should work too as tested
    conda activate mmcv  # make sure to activate environment before any operation
  3. Install PyTorch. Choose a version based on your need.

    conda install pytorch torchvision cudatoolkit=10.2 -c pytorch

    We only tested PyTorch version >= 1.6.0.

  4. Prepare MMCV source code

    git clone
    cd mmcv
  5. Install required Python packages

    pip3 install -r requirements.txt

Build and install MMCV

MMCV can be built in three ways:

  1. Lite version (without ops)

    In this way, no custom ops are compiled and mmcv is a pure python package.

  2. Full version (CPU ops)

    Module ops will be compiled as a pytorch extension, but only x86 code will be compiled. The compiled ops can be executed on CPU only.

  3. Full version (CUDA ops)

    Both x86 and CUDA codes of ops module will be compiled. The compiled version can be run on both CPU and CUDA-enabled GPU (if implemented).

Common steps

  1. Set up MSVC compiler

    Set Environment variable, add C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\bin\Hostx86\x64 to PATH, so that cl.exe will be available in prompt, as shown below.

    (base) PS C:\Users\xxx> cl
    Microsoft (R) C/C++ Optimizing  Compiler Version 19.27.29111 for x64
    Copyright (C) Microsoft Corporation.   All rights reserved.
    usage: cl [ option... ] filename... [ / link linkoption... ]

    For compatibility, we use the x86-hosted and x64-targeted compiler. note Hostx86\x64 in the path.

    You may want to change the system language to English because pytorch will parse text output from cl.exe to check its version. However only utf-8 is recognized. Navigate to Control Panel -> Region -> Administrative -> Language for Non-Unicode programs and change it to English.

Option 1: Build MMCV (lite version)

After finishing above common steps, launch Anaconda shell from Start menu and issue the following commands:

# activate environment
conda activate mmcv
# change directory
cd mmcv
# install
python develop
# check
pip list

Option 2: Build MMCV (full version with CPU)

  1. Finish above common steps

  2. Set up environment variables

    $env:MMCV_WITH_OPS = 1
    $env:MAX_JOBS = 8  # based on your available number of CPU cores and amount of memory
  3. Following build steps of the lite version

    # activate environment
    conda activate mmcv
    # change directory
    cd mmcv
    # build
    python build_ext # if success, cl will be launched to compile ops
    # install
    python develop
    # check
    pip list

Option 3: Build MMCV (full version with CUDA)

  1. Finish above common steps

  2. Make sure CUDA_PATH or CUDA_HOME is already set in envs via ls env:, desired output is shown as below:

    (base) PS C:\Users\WRH> ls env:
    Name                           Value
    ----                           -----
    <... omit some lines ...>
    CUDA_PATH                      C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v10.2
    CUDA_PATH_V10_1                C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v10.1
    CUDA_PATH_V10_2                C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v10.2
    <... omit some lines ...>

    This should already be done by CUDA installer. If not, or you have multiple version of CUDA tookit installed, set it with

    $env:CUDA_HOME = "C:\Program Files\NVIDIA GPU Computing Toolkit\CUDA\v10.2"
    # OR
    $env:CUDA_HOME = $env:CUDA_PATH_V10_2 # if CUDA_PATH_V10_2 is in envs:
  3. Set CUDA target arch

    # Suppose you are using GTX 1080, which is of capability 6.1
    # OR build all suppoted arch, will be slow
    $env:TORCH_CUDA_ARCH_LIST="3.5 3.7 5.0 5.2 6.0 6.1 7.0 7.5"


Check your the compute capability of your GPU from here.

  1. Launch compiling the same way as CPU

    $env:MMCV_WITH_OPS = 1
    $env:MAX_JOBS = 8  # based on available number of CPU cores and amount of memory
    # activate environment
    conda activate mmcv
    # change directory
    cd mmcv
    # build
    python build_ext # if success, cl will be launched to compile ops
    # install
    python develop
    # check
    pip list

    Note: If you are compiling against PyTorch 1.6.0, you might meet some errors from PyTorch as described in this issue. Follow this pull request to modify the source code in your local PyTorch installation.

If you meet issues when running or compiling mmcv, we list some common issues in TROUBLESHOOTING.

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