Privacy Policy

Last updated: November 4, 2026

The short version

• We collect only what we need to run the site: your email address if you join the newsletter or create a free account, and the settings and notes you choose to save in your account.
• We do not sell your email address or account information.
• We use Google Analytics to see how the site is used, and we show ads provided by Google and its partners. These use cookies, and you can opt out (see below).
• You can download a copy of your data or delete your account yourself from your account page, or ask us to do it.

Who we are

Engineer Underground (engineerunderground.com) is a free library of formulas, calculators, and references for engineers, makers, and students. It is operated by Engineer Underground, LLC, in the Phoenix, Arizona area. In this policy, “we”, “us”, and “our” mean Engineer Underground, LLC. This policy explains what personal information the site collects, why, who can see it, and what choices you have.

What we collect and why

Newsletter sign-up

When you enter your email address in the “Join the Underground” form, we store that address and the date, and send you a welcome email. We use it to tell you when new calculators, tools, references, and guides are released. To unsubscribe, reply to any of our emails with the word “unsubscribe”. If you sign up again with the same address, the site simply tells you that you are already signed up.

Free member accounts

When you create an account we ask for your email address and a password, and optionally your name. If you choose “Continue with Google” instead, Google sends us your name and the email address of your Google account (never your Google password), and we create or open your account with them. Your password is stored in scrambled (hashed) form that we cannot read. We use this information to log you in, to send you account emails (such as the welcome email), and to keep your saved settings. We are also notified by email when someone joins.

Paid memberships and payments

If you buy a paid membership, payment is handled by Stripe, a payment processor. You enter your card details on Stripe’s own secure page, so your card number never reaches or is stored on this site. We receive from Stripe your email address, a customer and subscription reference, which plan you chose, whether it is active, and when it renews or ends. We use this only to give you the features you paid for and to help with billing questions. Stripe’s use of your information is described in Stripe’s privacy policy. Our records of purchases may be kept as long as needed for tax and accounting.

Store orders

If you buy something from the store, we collect your name, email address, shipping address, optional phone number, and what you ordered. We use it to take payment, make and ship your order, send order and tracking emails, and handle problems. We share what is needed with Stripe (payment), our fulfillment partner Printful (printing and shipping your order), and the delivery carrier. You can check out as a guest without creating an account. We keep order records as long as needed for tax, accounting, and handling returns.

Downloads

When you download a table, formula sheet, practice set or calculator result, the site counts the download (a total for each item, not tied to you) and, for a free account, remembers that its one sample download has been used.

What you save in your account

If you are logged in, the site saves your choices so they are there next time, on any computer: the tabs you chose on Unit Conversions, and your My Dashboard workspace, meaning the widgets you added, where they are and how big, which ones you locked, their settings, the text you type into Notes, the place you choose for the Weather widget (its name and approximate coordinates), and your bookmarks, meaning the list of guides, tools and converters you press Bookmark on (kept as a list of page numbers, newest first, up to 200). If you add pictures to an Image widget, they are shrunk and stored in a private folder on the site’s server. They are never shown to other members or to the public, and they are deleted when you remove them from your dashboard or when your account is deleted. We use all of this only to show it back to you. As with any website, the site’s administrator can technically reach data stored in the site’s database.

Members can also save a calculation from a calculator. We then store the name you give it, an optional note, the calculator page, the values you entered (kept in the address of the saved page) and a short summary of the results, up to 100 saved calculations for each member. They are shown only to you on the My Calculations page and are deleted when you delete them or when your account is deleted.

Your profile and notification choices

On the Public Profile tab of your account page you can add a profile picture, a name, an industry and a short About text. All of these are optional except your name. There is no public profile page yet, so nothing there is shown to other people; if we open one later we will tell you first and you will be able to choose what is shown. A profile picture is cropped to a square, re-saved by us without any hidden information, and stored on our server. On the Notifications tab you choose which optional emails you would like (new guides and tools, membership and site news, store offers, and occasional feedback surveys). We save your choices and only send what you ticked; receipts, order updates and account security messages are always sent.

Groups

Members can create or join private groups with an invite code. A group stores its name and description, its invite code, who belongs to it and when they joined, the list of guides, tools and converters its members pooled in the shared workspace, and the short notes members post on its board, with the name you chose in your profile. Only members of a group can see any of this; it is not shown to anyone else on the site. If you leave a group you lose access to it, and the notes you posted stay there. If you delete your account you are removed from every group and your notes are deleted; if you owned a group it passes to its longest-standing member, or is deleted if nobody else is in it. As with any website, the site’s administrator can technically reach data stored in the site’s database.

Community forum

The community forum is public: anyone, including search engines, can read threads and replies. A post is shown with the name from your profile, your profile picture if you added one, a Staff or Member label where it applies, and your industry if you chose to make it public. We store what you write and when, the “Helpful” votes you give, the threads you follow, and any reports you send. A new member’s first post is held until the site owner approves it. The site owner can see who sent a report. If a post breaks the rules it may be hidden, and posting can be turned off for the member who wrote it. We email you about replies to threads you start or follow unless you turn this off under Notifications; you can also stop following a thread at any time. When you delete your own post, its text is erased and a note saying it was deleted remains. If you delete your account, your threads and replies stay so conversations still make sense, but your name is removed from them, and your votes, follows and reports are deleted. We count the posts you write, the Helpful votes you receive and the solutions you give into a points total, which sets a level name (for example Trench Digger) shown under your name. Other members see the level name only; the points total is private to you and is recalculated from your live posts, so deleting a post removes its points. Your forum posts are included in “Download my data”. As with any website, the site’s administrator can technically reach data stored in the site’s database.

Visitors without an account

If you use Unit Conversions without logging in, the tabs you choose are remembered in a small cookie on your own device (named eu_dash_tabs, kept for one year). It never leaves your browser except to be read by this site, and contains no personal information.

Technical and security information

Like most websites, our hosting provider records technical logs that include your IP address and browser details. A login-protection tool on the site records the IP address and username of repeated failed login attempts so that attackers can be blocked. If you ask for a password reset, your IP address is included in the reset email.

Comments

If a post on the site allows comments, we collect what you type in the comment form plus your IP address and browser details, to help detect spam. An anonymous string made from your email address may be sent to the Gravatar service to see whether you have a profile picture (Gravatar’s privacy policy).

Page views, page feedback and topic suggestions

To see which guides and tools are used most, we count visits to each guide and tool page. The count is a number per page per day, with no information about the visitor: no name, no IP address, and no cookie. A small note in your own browser (kept in local storage under a name starting “eu_fb_view_”) makes sure one browser is counted once per page per day. The counts decide which tools are shown as popular on the home page.

Each guide and tool page has a “Was this page helpful?” question. When you answer, we store which page, your answer (yes or no), the date, and any note you choose to add. We do not store your name, email address, or IP address with your answer. A small note is kept in your own browser so the question is not shown again on the same page. If you send a topic suggestion, we store what you wrote and the email address only if you choose to give one, and we use it only to answer you. To limit spam, your IP address is briefly used, in a scrambled form that cannot be turned back into the address, to count how many times something was sent in an hour; it is not kept with your feedback.

Contact form

If you write to us through the Contact page, we receive your name, email address, the topic you chose and your message, and we keep a copy in the sites database so we can answer you and follow up. We use it only to reply to you and to improve the site. The message is emailed to the site owner through the sites mail service.

The Weather widget

The Weather widget on My Dashboard uses Open-Meteo, a free weather data service. When you search for a place, your browser sends what you typed to Open-Meteo to find it. When the widget shows the forecast, your browser sends the place’s coordinates to Open-Meteo. Open-Meteo therefore receives your IP address, as any website does when you visit it (Open-Meteo’s terms and privacy information). If you choose “Use my location”, your browser asks your permission first; we then save the coordinates, rounded to roughly one kilometer, with your widget. You can change or remove the place in the widget’s settings at any time. Nothing is sent to Open-Meteo unless you add and set up the Weather widget.

Google: fonts, analytics, and ads

Fonts. The Inter typeface is served from this site’s own server, so your browser does not contact Google to display our fonts.

Analytics. We use Google Analytics, set up through Google’s Site Kit plugin, to understand which pages people visit, on what kind of device, and roughly where in the world visitors are (for example, city or country). Google Analytics uses cookies and similar technology to collect this information. Google uses your IP address to estimate your general location and does not store it. We use the results to improve the site, not to identify individual visitors. You can opt out with Google’s browser add-on.

Advertising. The site is supported by advertising. We show ads provided by Google and its advertising partners. Third-party vendors, including Google, use cookies to serve ads based on your previous visits to this site or other websites. Google’s use of advertising cookies enables it and its partners to serve ads to you based on your visit to this site and other sites on the internet. You can opt out of personalized advertising in Google’s Ads Settings, or through aboutads.info. To learn more about how Google handles information from sites like this one, see How Google uses information from sites or apps that use our services and Google’s Privacy Policy.

Cookies

Cookies are small files that a website stores in your browser. These are the ones this site uses. You can block or delete cookies in your browser settings; the site still works, but logging in and remembered tabs will not.

Cookie	Who sets it	What it is for	How long
wordpress_logged_in_…, wordpress_sec_…, wp-settings-…	This site	Keep you logged in and remember your screen choices. Set only when you log in.	Two days; two weeks with “Remember me”; removed when you log out
wordpress_test_cookie	This site	Checks that your browser accepts cookies on the login page.	Until you close your browser
eu_dash_tabs	This site	Remembers the tabs you chose on Unit Conversions.	One year
woocommerce_cart_hash, woocommerce_items_in_cart, wp_woocommerce_session_…	This site	Keep your shopping cart working as you move between store pages. Set only when you use the cart.	Until you close your browser; the cart session up to two days
__stripe_mid, __stripe_sid	Stripe	Help Stripe prevent fraud when you pay in the store.	One year and 30 minutes
_ga, _ga_…	Google Analytics	Tell visits apart so we can count them and see how pages are used.	Up to two years
Advertising cookies (for example IDE, DSID)	Google and its partners	Show and measure ads, and base them on your earlier visits.	Set by Google; typically up to about one year

Who we share your data with

We do not sell your email address or account information, and we share personal information only as needed to run the site:

• Our web host stores the site and its data on its servers.
• Our email service delivers the emails the site sends, such as welcome emails.
• Google receives the information described above for fonts, analytics, and ads.
• Open-Meteo receives place names and coordinates if you use the Weather widget.
• Anyone the law requires, if we are legally obliged to share information.

Other websites we link to, such as the sources we cite, have their own privacy practices.

How long we keep your data

• Newsletter information stays until you ask us to remove it. Account information stays until you delete your account.
• The settings and notes in your account stay until you change or delete them, or delete your account (see below). Records of store orders are kept for as long as tax and accounting rules require.
• Security and server logs are kept for a limited time and then removed.
• Google Analytics keeps its data for the period set in our account settings. Google controls how long ad cookies last.
• Comments, if any, and their details are kept until they are deleted.
• Daily page-view counts are kept for about a year. Page feedback and topic suggestions are kept for as long as they are useful for improving the site; ask us if you want a suggestion that contains your email address removed.

Your choices and rights

When you are logged in, the Privacy tab of your account page lets you download a copy of your account information (a JSON file) and delete your account for good. You can also change your name, email address, password, profile and notification choices there. You can still ask us at any time to send you a copy of the personal information we hold about you, to correct it, or to delete it. You can unsubscribe from the newsletter whenever you like, change or clear your saved dashboard and notes when you are logged in, and opt out of analytics and personalized ads using the links above. Depending on where you live (for example, in the European Union, the United Kingdom, or California), you may have additional legal rights, and we will respect them.

Children

The site is meant for a general audience of engineers, makers, and students. It is not directed at children under 13, and we do not knowingly collect personal information from them. If you believe a child has given us personal information, please tell us and we will delete it.

Keeping your information safe

We use an encrypted (HTTPS) connection, store passwords in hashed form, limit repeated failed logins, and keep backups. No online service can promise perfect security, so please choose a strong password that you do not use anywhere else.

Changes to this policy

If we change how the site handles personal information, we will update this page and the date at the top.

Contact us

You can download or delete your data yourself from the Privacy tab of your account page. To ask about your data, or if you cannot use your account page (for example, you have no account but are on our newsletter list), reply to any email we have sent you (such as your welcome email) and tell us what you would like. We will respond as soon as we can.