Circus Tent Sizing Calculator

This calculator treats a big-top as a set of concentric rings radiating out from a central performance ring, then works out how big the canopy over all of them needs to be. Tent radius is built additively: half the ring diameter, plus 0.75 metres of depth for every row of bench seating, plus a fixed 2-metre backstage corridor beyond the last row. Total floor area follows directly as a simple circle, pi times radius squared. Seating capacity isn't a flat density estimate — the calculator walks row by row, and because each row sits at a larger radius than the one before it, its circumference (and therefore its seat count) grows the further out you go.

For each row it takes the full circumference, subtracts the space eaten by however many aisles you specify (aisle count times aisle width), and divides the remaining arc by your chosen seat width to get seats in that row, then sums across every row. Centre pole height uses a traditional rule of thumb — roughly 0.6 times the tent's diameter, with a 6-metre floor — rather than a structural engineering calculation, so treat it as a starting point for a rigger, not a final spec. Fabric area is genuinely geometric: it treats the canopy as a cone, derives the slant height from pole height and tent radius via the Pythagorean theorem, and computes the curved lateral surface (pi times radius times slant height) — it does not add extra for sidewalls, doors, or overlap/seam waste, so budget more raw fabric than the number shown. The seat-width and aisle inputs matter more than people expect: narrowing aisles or seats by even a few centimetres compounds across every row and can add or remove dozens of seats.