How to change size of figure with subplots

You can remove your initial plt.figure(). When calling plt.subplots() a new figure is created, so you first call doesn’t do anything.

The subplots command in the background will call plt.figure() for you, and any keywords will be passed along. So just add the figsize keyword to the subplots() command:

def plot(reader):
    channels=[]
    for i in reader:
        channels.append(i)

    fig, ax = plt.subplots(len(channels), sharex=True, figsize=(50,100))

    plot=0    
    for j in reader: 

        ax[plot].plot(reader["%s" % j])
        plot=plot+1

    plt.tight_layout()
    plt.show()