06Manhole covers: shapes, letters and what's underneath

The short version: A manhole cover is a removable lid over a shaft that lets workers reach sewers, drains, water, gas, power or phone lines. Most are round, cast iron and heavy - typically 200-300 lb (90-136 kg) - and the raised letters on top tell you what is underneath and who owns it.⁸⁵ Because covers last for decades, many still carry the names of utilities that merged or vanished long ago, which makes them small, readable pieces of city history.⁸⁶ Do not lift, pry at or step on a rocking cover, and keep clear of an open one; report it to the city instead.

Why are manhole covers round?

What you see: A heavy round metal disc, about two and a half feet across, flush with the road or sidewalk, with a raised grip pattern and lettering.

There is no single answer, and Live Science says so plainly.⁸⁵ The reasons usually given:

• The openings themselves are round, because they are cut with rotating tools.⁸⁵
• A round cover cannot fall through its own opening however it is turned. A square one can, if it is tipped and dropped along the diagonal.⁸⁵
• A round cover can be rolled instead of carried.⁸⁵
• A round cover uses less material than a square one of similar width.⁸⁵

A round lid also seats in its frame at any angle, so a worker does not have to line it up. The question became famous as a Microsoft job-interview prompt, meant to draw out creative answers rather than one correct one.⁸⁵

Size is set by the person going down, not the pipe. Modern openings have to be big enough for a worker wearing breathing apparatus, which is why Nashua, New Hampshire, was switching to a 31.5-inch (80 cm) round cover as of 2011.⁸⁷

Look closely at older covers for small working details. In old New York sidewalks, for example, each cover has a half-inch groove that steers water toward the gutter.⁸⁸

Covers are also rated for the traffic they carry. In Europe, the EN 124 standard sorts them into classes by test load, from A15 (15 kN, pedestrian-only areas) through D400 (400 kN, road carriageways) to F900 (900 kN, aircraft pavements).⁸⁹ In the US, cities write the rating into their own specifications: Tomball, Texas, for example, requires castings that withstand AASHTO HS-20 truck loading without permanent deformation and gives 32 inches as the standard cover diameter.⁹⁰ Kirkland, Washington's standard sewer manhole calls for a locking ring and cover with a 24-inch clear opening.⁹¹

Why are some covers square, rectangular or triangular?

What you see: A square or rectangular lid, often smaller than a manhole and sometimes hinged. Very rarely, a triangular cast-iron lid.

A non-round lid usually sits over a shallow box or a long vault that nobody climbs into: a valve, a meter, a cable splice. Rectangles suit cable chambers. In the UK, telephone footway covers are generally concrete with steel or cast-iron reinforcing around the edges, while covers in the roadway are cast iron.⁹²

Triangles are the oddity. Nashua Foundry began casting triangular sewer covers in the 1920s or 1930s at the suggestion of engineer Walter Ellis, who thought they would rattle less than round ones.⁸⁷ They were laid pointing in the direction of sewer flow, which helped crews find problems.⁸⁷

The 25.5-inch (65 cm) triangles weigh at least 150 lb (68 kg), but they are too small for a worker in breathing gear, so as of 2011 the city was replacing 100-200 a year, out of about 7,500 sewer manholes, with 31.5-inch round covers.⁸⁷ The Nashua Telegraph found no other city with triangular sewer covers; the closest it found was water valve covers in a San Francisco development.⁸⁷

A small triangular lid at a gas station is something else entirely: usually an environmental monitoring well, covered in small lids and grates.

What do the letters on a manhole cover mean?

What you see: Raised letters such as "SEWER", "DRAIN", "WATER", "GAS", "ELEC", "TEL", a set of initials, and often a second, smaller name and a year.

Read a cover in three layers:

Covers can record former local authorities and long-gone companies, which is why historians treat them as evidence. Enthusiasts who photograph and study them are sometimes called gridders.⁸⁶

Foundry names are the small print. Neenah Foundry of Neenah, Wisconsin, founded in 1872 as Aylward Plow Works, makes cast-iron manhole covers, gratings and tree grates, and its name is common on US covers.⁹³ Pont-à-Mousson, whose name is on many Paris covers, dates from 1854 and merged with Saint-Gobain in 1970.⁹⁴ In the UK, telephone covers are marked with type number, date and manufacturer, either on a plate in the concrete face or cast on the underside.⁹²

The utility words are mostly self-explanatory, though the exact labels vary from city to city and utility to utility.

In Boston: a cover decoder

What you see: Initials like BWSC, BWW, B.C.G.Co or N.E.T.&T. Co. on covers around downtown, Chinatown and the Back Bay.

Boston's covers are a layered record of mergers (the Boston section collects the city's other street oddities). The table below lists what has been documented by Forgotten New York's Boston visit and by Universal Hub and its readers.

Universal Hub readers also report covers lettered METWW, CELCo, MassDPW, MassHighway and MassDOT electrical covers, and fiber covers from MCI, MFS McCourt and Level 3.⁹⁶ These come from reader comments, and the meanings of METWW and CELCo are not confirmed.

Electric covers follow the same pattern. Forgotten New York reported in 2015 that many Boston electric manholes still read "E.E.I.Co", that covers replaced later say "Boston Edison Company" or "B.E.Co.", and that no NSTAR-owned manhole in Boston carried the NSTAR name.⁹⁷

Boston's 311 system has a "Sidewalk Cover / Manhole" request type, filed under Sidewalk. In one December 2025 report of a loose sidewalk cover on Batterymarch Street, the case went to the Boston Water and Sewer Commission and was closed in February 2026 as "Sealed loose cover."⁹⁸

How heavy is a manhole cover, and why do people steal them?

What you see: Usually nothing, because the giveaway is a missing cover: an open hole ringed with cones, a plywood patch, or a plastic or composite lid where iron used to be.

Cast iron or concrete covers generally weigh 200-300 lb (90-136 kg).⁸⁵ Small ones can weigh less - Nashua's triangles weigh at least 150 lb (68 kg) - and heavy-duty traffic covers weigh more: Iowa's DOT specifies at least 320 lb (145 kg) for a ring and cover in a traffic area.⁸⁷⁹⁹

That weight is worth little as scrap, but theft spikes when metal prices rise. In 2008 Long Beach, California lost 80 covers in a few months after losing one in the years before; Philadelphia estimated up to 10 a day; Chicago lost 200 in a month; and Cherokee County, Georgia lost 30 in two weeks.¹⁰⁰ One stolen Long Beach cover weighed about 215 lb (98 kg), and recyclers paid only about $10-15 a cover.¹⁰⁰ Historic coal-hole covers in Britain are at risk of theft too.⁸⁶

A missing cover is a fall hazard for anyone, and in the road it can damage a car or throw a cyclist. If you see one, keep people away from it and report it to the city or the utility named on nearby covers, through your city's non-emergency line (see the sister guide's 311 section), or call 911 (or your local emergency number) if it is in a travel lane.

Why do manholes smoke or explode in winter?

What you see: Smoke or flames coming out of a manhole, a cover blown into the air, or a cover with holes or slots that is latched in place.

This is a short pointer; the electric section of the sister guide covers the system. Underground electrical cables fail, often when salty snowmelt gets into aging insulation, and the arcing produces heat and combustible gas that can lift or launch a cover.¹⁰¹ The New York Fire Department logged nearly 4,000 manhole explosion dispatches and more than 45,000 manhole emergencies from 2009 to 2018; in January and February that came to about three explosions a day.¹⁰¹

The main fix you can see is the vented cover, a lid with slots or holes that lets smoke and gas escape instead of building pressure. Con Edison had installed about 100,000 of them by 2015, with about 150,000 to go at roughly 10,000 a year.¹⁰² Con Ed has also installed 21,500 miles (34,600 km) of corrosion-resistant cable, gas monitors and latching vented covers.¹⁰¹ It opposed chaining covers down, warning that a restrained cover could shatter "like shrapnel."¹⁰² If a manhole is smoking, move well away and call 911 or your local emergency number.

What is the orange-and-white steam tube in New York?

What you see: A tall orange-and-white striped tube standing on a manhole in a New York street, with steam pouring from the top.

Con Edison runs a district steam system under Manhattan. Service began in March 1882 in the Financial District, and it is the largest steam system in the US, with about 105 miles (169 km) of pipe serving more than 1,500 buildings, about 250 of which use steam for summer cooling.¹⁰³ The steam is delivered at 450-475°F (232-246°C), and the fuel is about 97% natural gas.¹⁰³

When steam or vapor escapes underground, from a leak or from water hitting hot pipe, crews set up a stack to carry it above cars and people. Con Ed says such conditions are controllable and "not a safety issue."¹⁰³ See the gas and steam section of the sister guide for how district steam works.

Boston has its own district steam system, run by Veolia. A 2014 Veolia brochure said it served 250 customers, including 70% of Boston's high-rise buildings, and about 44 million square feet of buildings in Boston and Cambridge.¹⁰⁴

Why are Japan's manhole covers so decorative?

What you see: A cover cast with a local landmark, festival, flower, mascot or cartoon character, sometimes painted in full color.

Japanese towns design their own sewer covers as civic art. The idea is credited to Ministry of Construction official Yasutake Kameda, who proposed letting municipalities design their own covers to build public support for expensive sewer connections. Neocha puts the count at more than 6,000 custom designs.¹⁰⁵ Commercial designs exist too: Sanrio Puroland unveiled 10 Hello Kitty manholes in late 2017.¹⁰⁶

How do I get Japanese manhole cards?

What you see: A trading-card-sized card with a photo of one town's cover on the front and its location and design story on the back.

Manhole cards are issued by GKP (Gesuido Koho Platform, the Sewerage PR Platform), a group set up in fiscal 2012 to promote sewerage.¹⁰⁷ You collect them in person at designated sites. Tokyo's Bureau of Sewerage, for example, hands them out at five locations, including the Tokyo Sewerage Museum "Rainbow", with a different design at each.¹⁰⁸

Sources for the table: GKP (2016 and 2018 rows) and Japan's Ministry of Land, Infrastructure, Transport and Tourism (2023 rows).^109110107 The 19th release included the first card from outside Japan, for Siem Reap, Cambodia.¹¹⁰ Releases have continued since 2023. GKP's 29th release, announced for summer 2026, added 46 designs from 45 municipalities, bringing the total to 1,311 designs from 783 municipalities and 4 organizations; its overview does not give a cumulative print count.¹¹¹ Check GKP for the current list before planning a trip around one.

The Japan Times dates the shift to designer covers to the 1980s, when only about 60% of Japanese households were connected to municipal sewers.¹¹²

Elsewhere in the world

What you see: In Britain, rectangular covers marked "GPO", "PO" or "BT". In Berlin, a cover crowded with city landmarks. In Paris, cast-iron rings and a foundry name with a picture of a bridge.

United Kingdom. Before British Telecom, the General Post Office ran Britain's phones, and its covers are still everywhere. GPO "Joint Box" covers, later renamed "Covers, Footway", go back to Joint Box Cover 3 in 1904.⁹² Cover type 4A was "marked BT in 1982", and driveway covers came in around 1983.⁹² Early roadway covers were a cast-iron lattice filled with wooden blocks, and some covers have vents or locks.⁹² A joint box is a shallow box where cables are spliced, the British equivalent of a US handhole.

Berlin. Berlin's relatively new Kanaldeckel (sewer covers) show a montage of landmarks. An NPR blogger picked out the Olympiastadion, the Gedächtniskirche, the Reichstag, the Fernsehturm, the Brandenburg Gate and the Siegessäule, and the water utility, Berliner Wasserbetriebe, confirmed that the jumbled one is the Bundeskanzleramt.¹¹³

Paris. A street cover is a regard de chaussée or plaque d'égout.⁹⁴ The Pont-à-Mousson logo shows the bridge over the Moselle at Pont-à-Mousson, which was destroyed in World War II; another maker was the Paris foundry of Noël Chapadaux, which held an 1878 patent.⁹⁴ Some small Paris covers open onto a building's water valve, turned with a long-handled tool, and others onto the gas pipe serving a building.⁹⁴

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