Sonotube calculator

Sonotube is the trade name contractors still type when they mean a cardboard concrete form tube: a round, single-use mold that stands on a footing or grade and takes a pour of ready-mix or bagged concrete for a deck pier, porch column, mailbox stem, or lamp post. Ordering the mix starts from cubic yards, not from a diameter printed on the carton, and a Saturday bag run starts from how many 80-pound sacks that yardage equals. This Sonotube calculator takes tube diameter in inches, fill height in feet, and how many identical tubes you will stand, models each form as a right circular cylinder, and returns cubic yards plus the equivalent 80-pound bag count using the published 0.60 cubic-foot yield.

How Sonotube fill volume becomes cubic yards and bags

A Sonotube form is a right circular cylinder that you fill to the top, so the concrete volume is the classic pi r squared h of a solid cylinder — not an annulus around a buried post, not a hollow cardboard shell, and not a rectangular footing. Tube diameter is entered in inches because that is how cardboard form tubes are sold: eight, ten, twelve, sixteen, eighteen, and twenty-four inch cartons are the common SKUs on a lumber-yard rack.

Fill height is entered in feet because that is how tube lengths and pier heights are quoted: a four-foot, eight-foot, or twelve-foot stick, or a cut-down height to the underside of a beam. Radius in inches is diameter divided by two; height in inches is height in feet times twelve; volume of one tube in cubic inches is pi times radius squared times that height. Total cubic inches multiplies by the integer quantity of identical tubes.

Cubic feet divide the cubic-inch total by 1,728; cubic yards divide it by 46,656, which is the same as dividing cubic feet by twenty-seven. Equivalent bag count uses the published yield of an 80-pound sack of bagged concrete, 0.60 cubic feet, and takes the ceiling so you never round down a fractional sack at the store. A classic check is one twelve-inch tube, four feet high: radius is six inches, volume is pi cubic feet, about 0.116 cubic yards, and six 80-pound bags after the ceiling.

The path is deterministic floating-point arithmetic with no random seeds, no wall-clock timestamps, and no network. Quantity, when sent, must be a positive integer; omitted quantity defaults to one tube. Waste, over-excavation, and flared bells are not added; apply those percentages after you have the geometric volume of the filled forms.

Where a Sonotube calculator earns its keep

Deck builders and remodelers reach for a Sonotube calculator when the ready-mix desk or the bag aisle asks for cubic yards, not a carton diameter. Knowing the tube size, how tall each pier will stand, and how many identical forms you will set yields a fill volume you can compare against a truck minimum and a bagged-mix backup without opening a spreadsheet of pi. Porch, carport, and raised-cabin crews use the same three numbers to size a small mixer and avoid a short load on a Saturday.

Mailbox, lamp-post, and sign contractors need a reproducible yardage from the same fields an inspector can read off the submittal. Estimating desks that already count piers from a plan still need a second, distinct volume for the concrete line item; counting posts and filling cardboard tubes are different search intents and should not share a page. This landing is also not a generic cylindrical column in matching linear units, not a post-hole collar that subtracts buried lumber, and not a rectangular slab or pad-footing takeoff.

Trade-school modules on construction takeoff can pin the twelve-inch by four-foot single tube in tests because the arithmetic is deterministic. If you only need a unit-agnostic cylinder, that is a different calculator; if you are pouring around a post in an augered hole, subtract the post instead of filling a form.