Four panels, and the mouth is the smallest of them
A box-style goal net is a roof, a back and two sides. The roof is the goal width times the top depth. The back runs from the crossbar down to the rear ground bar, so its height is not the goal height but the slant: the square root of the goal height squared plus the difference between the two depths squared. The sides are trapezoids, each with a short parallel edge at the top depth and a long one at the ground depth, so the pair together is the goal height times the sum of the two depths.
On a 24 by 8 foot mouth with a 3 foot top and an 8 foot bottom, the slant is the square root of 64 plus 25, which is 9.43 feet. The back is 226.4 square feet, the roof is 72, the two sides are 88. That is 386.4 square feet against a 192 square foot opening — 2.01 times the mouth.
| Panel | Formula | Sq ft on the defaults |
|---|---|---|
| Roof | width x top depth | 72.0 |
| Back | width x slant | 226.4 |
| Two sides | height x (top + bottom depth) | 88.0 |
| Total | 386.4 |
Add ten percent for the slack a net has to hang with and the cut edges, and one goal is 425.1 square feet. Two goals is 850.1, which is 94.5 square yards.
The run-back is what decides whether the field fits
People measure the field and forget that the goals stick out behind the goal line, and that there has to be clear ground behind them as well. On the defaults, the net runs 8 feet back and the facility wants 12 feet clear behind that, so each end needs 20 feet beyond the goal line. A 330 foot field therefore needs 370 feet of ground, not 330. With 375 feet available there are 5 feet spare, and that margin is the whole difference between a field that works and a fence somebody keeps running into.
The clear space figure is a field on this page rather than a number, because run-off and safety margins are set by the organisation that sanctions your play and by your own facility standard, they differ between levels and between sports, and they change. What the calculator does is arithmetic against the figure you supply. Whether the margin that comes out is acceptable is not something a form can rule on.
Anchor positions are a layout, not a specification
Goals tip over. A portable goal is a heavy frame with most of its mass high up and a small footprint, and a child hanging on the crossbar can bring it down. People have been killed this way, repeatedly, and it is the single most serious hazard on any field this site has a calculator for.
What holds a goal down depends on the goal, the ground and the product, and it is answered by the instructions that came with the goal and by the manufacturer. This page will not tell you what anchor to use, how many, how deep, or whether what you have is enough, and the positions it counts are marks on a layout drawing rather than a specification. The count comes from dividing the ground frame run by the spacing you enter and adding one for the far end. That is all it is.
The one thing worth stating plainly with no arithmetic attached: an unanchored portable goal is the hazard. Goals that are not in use and not secured do not belong where anyone can reach them.
Netting is ordered loose
A net that measures exactly its panel area will not fit. Nets hang with slack so that a ball is caught rather than bounced back out, and every edge is trimmed and tied. Ten percent is a starting allowance; a net being made up from flat stock with a lot of cutting wants more. The waste percentage is a field so you can price what your supplier tells you they need.
What this page will not decide
Goal sizes are rule-book dimensions. They differ by sport, by age group, and by the body sanctioning your games, and small-sided formats use several sizes within a single club. Measure the goals you have, or take the size from the document that governs your play.
Why no dimension on this page is a specification
Every distance here is something you type in. That is deliberate. Base paths, arc radii, goal sizes, line widths, run-off margins and safety zones are not universal numbers: they differ between youth, high school, college and adult play, between the organisations that sanction those games, and between one facility standard and the next. A page that hard-coded any of them would be wrong for most of the people reading it and would sound authoritative while being wrong.
So the rule book that governs your league is the authority on the dimension, and the facility standard your grounds department works to is the authority on how much room goes around it. Measure the field you actually have, take the target dimensions off the document that governs your play, and put those numbers in the form. What this calculator does is the arithmetic that follows.
Before anything goes into the ground
Irrigation mains, drainage, electrical runs to scoreboards and lighting, and old utility crossings all live under sports fields, frequently at shallow depths and frequently not where the as-built drawing says. Call 811 before you dig, trench, drive a stake, auger a post or set an anchor, and give the locate time to be marked. Private lines on the facility side of the meter are usually not covered by the public locate service, which is what catches out a crew that did everything else right.
Open fields are also the place people get hurt by heat and by machinery. A groundskeeper on a mower or an aerator in July is exposed on both counts at once, and neither risk announces itself.
Related pages: the backyard court size calculator works the same fit problem for a court, the sport court fence calculator handles perimeter fabric and backstop netting, the batting cage net calculator sizes a cage, and the field marking paint calculator covers the lines on the same field.
Questions people ask
How many square feet of netting does a goal need?
Add four panels. Roof is width times top depth. Back is width times the slant, which is the square root of the goal height squared plus the difference between the two depths squared. The two sides together are the goal height times the sum of both depths. On a 24 by 8 foot mouth with a 3 foot top and 8 foot bottom that is 72, 226.4 and 88, or 386.4 square feet — about twice the area of the opening.
How much space do I need behind a goal?
At minimum the net depth at the ground, plus whatever clear space your governing body and facility standard require behind that. On the defaults here the net is 8 feet deep and the clear space entered is 12, so each end takes 20 feet beyond the goal line and a 330 foot field needs 370 feet of ground. The clear space figure has to come from your rule book, not from a calculator.
Why is the goal net so much bigger than the goal?
Because three of its four panels are not in the plane of the mouth. The back panel is the largest single piece and it is taller than the goal itself, since it runs on a slant from the crossbar down to a ground bar several feet behind the line. On the defaults the back alone is 226 square feet against a 192 square foot opening. That ratio is why net prices surprise people.
How do I anchor a portable goal?
This page does not answer that, deliberately. Goal tip-over has killed children, and the anchoring that holds a particular goal in particular ground is specified by the manufacturer of that goal in the instructions supplied with it. What kind of anchor, how many, and whether an installation is adequate are questions for those instructions and for the manufacturer. What is safe to say without any qualification is that an unanchored goal is the hazard, and one that is not in use and not secured should not be left where anyone can reach it.
How much extra netting should I order?
Enough that it hangs loose. A net stretched to its exact panel dimensions rebounds balls back into play and puts load on every tie point. Ten percent is a reasonable starting allowance and it is a field here so you can use whatever your supplier says they need for cutting and finishing. Nets made up from flat stock with a lot of shaping generally want more than nets supplied as a finished shape.