Lob Help Center


Checks overview

To get started with sending checks, you'll need to setup and verify an account, in your Bank Accounts section, to originate checks from. Once you have setup your bank account, visit our Checks API documentation, GitHub library, or our Template Gallery for ideas on how to get started.

Check dimensions & specs

The specifications for Lob's check product are as follows:

  • Measures 8.5 x 3.625" in size
  • Printed on bank-grade chemical reactive paper (with watermarks, warning bands)
  • Paper is perforated with the bottom ⅔ of the page available for the sender to customize with artwork
  • Includes a three-dimensional graphic foil that is embedded into the check, along with fugitive ink, to provide additional protection against duplication of the document
  • Includes a prismatic multicolored background with subtle graduations to make copying and reproducing difficult
  • Produced with controlled stock, which ensures the security of the mail piece at every stage of production. The Padlock Icon printed on the checks ensures that the product meets or exceeds industry guidelines.
  • Mailed in a Standard #10 white outer envelope (double-windowed)

Note that logos and branding can be added to checks via an API request, but cannot be added through the dashboard. For more details on the space your logo can take up, visit our API documentation.

Check front:
Check back:

Mailing checks

Ensure your checks get to their final destination by following these guidelines:

  • The from field is required for all checks, regardless of the destination
  • Checks can only be mailed using First Class Mail (takes 4 to 6 business days)
  • USPS Standard Class Mail (or Marketing Mail) is not available for checks
  • Overnight mailing options are not available for checks

Check with your bank

Check with your bank to make sure that the check will be accepted. A new check template or different signatory can cause the bank to flag your account. The best way to avoid this happening is to let your bank know that the checks are valid.

Your money is not transferred to Lob. When the payee deposits the check that was sent through Lob's Checks API, it will pull money directly from the specified bank account into the recipient's bank account.

Verifying your bank account

Lob will send two micro-deposits, ranging from 1 - 100 cents, to the specified bank account in order to verify the account. You'll be asked to enter them in the dashboard or submit them through the API before you can send out any checks.

This is especially important if you are sending checks on behalf of your customers. You must verify all your customers' bank accounts before sending checks from them. This is most easily done through the API.

Note: Lob's Check service only works with US banks, based on US banking standards and formats. We do not support foreign bank accounts at this time.

Fraudulent activity

Our security team continuously reviews newly-created accounts. New accounts that trigger a flag will be immediately suspended and required to provide additional verification.

If you have any questions or concerns, contact us.

Uploading a signature for checks

One of the options for associating a custom signature to a bank account, so that it can be printed on checks, is uploading an image file during the initial bank account creation process. You can add a signature to the new bank account creation page in the Lob dashboard. 

Signature image file 

The uploaded signature will be printed on all Lob checks originating from that specific bank account. Make sure to download the digital signature and authorize its use with your bank once your bank account is created.

If you would like to upload a new custom image file as a signature anytime after the initial creation of the bank account, you must reach out to support@lob.com with:

  • The bank_account_id of the bank account the signature corresponds with
  • A PNG of the signature (the background of the image must be transparent)

Below are the guidelines to adhere to when prepping your image so that the signature can best be extracted and processed.

Image format

The image must be in either a JPEG or PNG format (.jpg, .jpeg, .png). The background of the image must be transparent.


The image must be at least 330px x 105px. The image may be larger but we recommend a width to height ratio of approximately 3:1 for best results.

Color and size

The signature must be written in black or dark ink on a white or light background. The signature should be centered and should occupy most of the image.

Things to avoid

Here are a few of the most common mistakes that we recommend you avoid when preparing a signature image.


Make sure to center your signature and crop your image as needed so that the signature takes up a majority of the space.


Write your signature on a white or light-colored background to ensure proper signature processing. Using ruled or patterned paper will likely result in unintended artifacts.


If you are taking a photo of your signature rather than using a scanned image, make sure to prepare your photo so that all artifacts and non-signature objects (e.g. tables, pens, dark shadows) are cropped out.

Customizing check pages

It is possible to send a letter as an attachment with your check (but not the other way around). These check pages do not require any artwork in order to be sendable; however, it is a great opportunity to leverage the blank space at the bottom of the check to add any branded artwork or personalization. 

If you choose to customize this optional section, be sure to follow the provided template and leave room for the actual check itself; otherwise you risk invalidating the check. You may also add up to 3 sheets (6 double-sided pages) of optional attachment pages. 

See our Checks API documentation for more details on the attachment parameter, or see the Template Gallery for design inspiration.

Check bottom template:

Customized check example:

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