A pane can be cut within a supplier’s stated tolerance and still be the wrong size for your greenhouse. The important step is agreeing what size should be ordered for the frame, material and position involved. Once that is settled, the cutting tolerance explains the supplier’s permitted variation around the ordered dimensions.
Keep three entries in your planning notes: the measurement you recorded, the size you are asking about, and the order size confirmed by the supplier. This makes the conversation much easier to follow if a dimension changes.
What cutting tolerance means
Simply Plastics currently lists a cutting tolerance of ±1 mm for its replacement polycarbonate greenhouse glazing. For an illustrative ordered width of 600 mm, that stated tolerance represents a width from 599 to 601 mm. Check the current specification for the actual product before ordering. Supplier’s polycarbonate specifications
That figure describes the cutting service. It gives you no answer, by itself, about whether 600 mm is suitable for your frame.
What a fitting allowance means
A fitting allowance is the difference needed between the relevant frame dimensions and the finished pane for a particular glazing system. Ask the manufacturer or supplier to confirm it. Applying the same deduction to every greenhouse and material would turn an unresolved question into a confident-looking number.
Material behaviour can matter too. Palram explains that its PALSUN solid polycarbonate expands more with temperature than glass and that this must be considered when mounting the sheets. Its data sheet covers that product; use the relevant manufacturer’s guidance for the material you are considering. Palram PALSUN data sheet
Keep thickness separate
Width, height and thickness need their own checks. A cutting tolerance for the outline of a sheet is separate from a manufacturer’s thickness tolerance. Ask whether the proposed thickness works with the frame, clips, seals or other components already fitted.
A useful question is: ‘These dimensions were recorded from the frame opening. What finished pane size and thickness should I order, and what variation can your cutting service supply?’ Include photographs and the greenhouse model where available.
Leave uncertain sizes visibly uncertain
Use a note such as ‘order size awaiting supplier confirmation’ until you have a clear answer. Keep a triangular or other shaped pane on its own drawing or enquiry line, with the orientation identified.
Once the supplier confirms the specification, save it alongside their quotation. Check that later quotes refer to that same specification. The point of the record is to reduce misunderstandings before purchase, rather than promise that an automatically calculated size will fit.
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