How much glass do you actually need for a Hobart window job?
One sash of a typical Hobart double hung window is about 900 x 700, which is 0.63 square metres, and a window has two of them. A whole 8 window house is usually 6 to 10 square metres across 10 to 16 panes. Size the job first with the calculator below, then read the measuring method, because measuring the old pane instead of the rebate is how people end up buying toughened glass twice.
Size the job, then price it.
Set the total area and the number of separate panes. The area is the glass itself, the pane count is how many separate pieces have to be cut, carried and fitted, and both move the price independently. This is a sizing tool: for a straight cost comparison across every service, use the Hobart glass repair cost guide.
What this estimate assumes.
- Glass supplied, cut to size, delivered and fitted into an existing sound frame in Hobart or the southern suburbs, in 2026.
- The per pane rate falls as the count rises: twelve panes in one visit is much cheaper per pane than one pane on its own, which is why the tool prices area and pane count separately.
- Excludes repairing rotten timber, painting, plastering, new frames and any electrical or plumbing work.
- Excludes a minimum call-out of $120 to $180 on very small single pane jobs, which we tell you about before booking.
- Sealed unit retrofits assume the rebate is deep enough. If it is not, tick the rebate option, which is the joinery, not the glass.
- A firm price needs a measure. On anything toughened we template on site, because toughened glass cannot be trimmed later.
How to measure it properly with a tape and a phone.
Ten minutes with a tape turns a vague enquiry into an accurate indicative price. You are not measuring to order glass, we do that, you are measuring to know what you are dealing with.
- Measure the rebate, not the pane. The rebate is the recess in the frame the glass sits into, behind the putty or the bead. Old panes were often cut small, and copying one just repeats an old mistake.
- Three readings each way. Width at the top, middle and bottom. Height at the left, middle and right. Write down the smallest of each. Older Hobart joinery moves, and a 20mm difference top to bottom is common in a settled weatherboard.
- Check the diagonals. Corner to corner both ways. If they differ by more than about 5mm the opening is out of square, which matters enormously for a shower screen or a splashback and hardly at all for a puttied sash.
- Measure the rebate depth. Push the tape into the recess. You need the glass edge properly covered, and for a sealed unit you need real depth. This one number decides whether a double glazing retrofit is simple or a joinery job.
- Work out the existing thickness. Look at the exposed edge of the glass where it meets the putty, or hold a phone torch at an angle and count the reflections. If you cannot tell, photograph the edge with a coin next to it.
- Look for the safety glass stamp. A sandblasted or printed mark in a corner naming the maker and a standard means toughened or laminated. No mark means assume plain float, which matters if the pane is in a door or near the floor.
- Photograph everything. One wide shot of the whole window from inside, one from outside, and one close up of the corner with a tape in the frame. Those three photos plus your numbers are enough for us to quote without visiting.
- Convert to square metres. Width in millimetres times height in millimetres, divided by one million. So 900 x 700 is 630,000 divided by 1,000,000, which is 0.63 square metres.
Got your numbers? Send them through.
Rough sizes and three photos are enough for an indicative price, usually the same business day, and the on site measure is free.
Rules of thumb, clearances and safety allowances.
- Clearance. Float glass in a timber rebate is normally cut about 2mm to 3mm under the rebate size on each dimension so it can be bedded without binding. Glass expands and contracts, and a pane cut tight will crack the first cold snap after a warm afternoon.
- Edge cover. The rebate has to hold enough of the glass edge to keep it in place under wind load. That is why rebate depth is on the measuring list, and why a 24mm sealed unit does not simply drop into a rebate designed for 4mm glass.
- Thickness by area, as a sanity check. Up to about 0.5 square metres, 4mm. From 0.5 to 1 square metre, 5mm or 6mm. From 1 to 2 square metres, 6mm. Above 2 square metres, or anywhere exposed, 6.38 laminated or thicker. AS 1288 does the real calculation from pane area and design wind pressure, and on an exposed Hobart site that calculation often lands a step above the rule of thumb.
- Wind exposure is a Hobart specific. A sheltered New Town courtyard window and a west facing window on Mount Nelson or an open block above Kingston are not the same engineering problem, even at the same size. Tell us how exposed the wall is.
- Safety glass allowance. Doors, side panels next to doors, low windows near the floor, bathrooms and shower enclosures need Grade A safety glass under AS 1288 regardless of what is in there now. Budget the toughened or laminated rate for those openings, not the float rate. Details on our AS 1288 page.
- Wastage. On cut to size glass, offcuts are the supplier problem, not yours, so there is no wastage percentage to add. The exception is a job where you are matching an unusual obscure pattern or a heritage restoration glass, where we may need to buy a full sheet to get two panes out of it. We tell you when that applies.
- Spare panes. If you have four identical windows in a rental and one keeps getting broken, ordering a fifth pane with the batch costs the glass only, roughly $60 to $140, and saves a whole call out later.
The sizing mistake that costs the most here.
It is not getting a millimetre wrong on a puttied sash. That is recoverable, because float glass can be recut in the van. The expensive mistakes are these three, in order.
- Ordering toughened glass from a customer measurement. Toughened glass is cut and drilled before heat treatment and cannot be touched afterwards. A shower panel 5mm too wide is not adjustable, it is scrap, and someone pays for it twice. On a frameless screen or a splashback that is $400 to $1,200 gone. Anything toughened gets templated on site, always.
- Assuming a sealed unit fits an old rebate. A double glazed unit is commonly 18mm to 24mm thick. A 1930s Hobart timber sash rebate cut for 4mm glass may be 10mm to 14mm deep. Deepening the rebate and fitting new beads is $150 to $400 per sash, which on a whole house is a $1,200 to $3,200 difference between a quote that accounted for it and one that did not. Measure the depth before you compare prices, and see heritage sash reglazing if the sashes are original.
- Sizing to the old pane in a settled house. If a previous repair was cut short and packed with putty, copying it leaves the same gap, and in a Hobart winter that gap is a draught you will feel from the couch.
Worked example: a 1930s weatherboard in Moonah.
Eight windows, mostly original timber double hung sashes, ground floor, easy access, owner wants every pane replaced with clear float and the two compliance sensitive openings done properly. Here is the arithmetic, exactly as we would do it at the kitchen table.
| Opening | Pane size | Panes | Area |
|---|---|---|---|
| Living room double hung | 900 x 700 | 2 | 1.26 m² |
| Dining double hung | 900 x 700 | 2 | 1.26 m² |
| Kitchen awning | 1000 x 600 | 1 | 0.60 m² |
| Bedroom 1 double hung | 800 x 650 | 2 | 1.04 m² |
| Bedroom 2 double hung | 800 x 650 | 2 | 1.04 m² |
| Bathroom, obscure glass | 600 x 500 | 1 | 0.30 m² |
| Front door sidelight, needs Grade A | 400 x 1500 | 1 | 0.60 m² |
| Laundry | 700 x 500 | 1 | 0.35 m² |
| Total | 12 | 6.45 m² |
Put 6.5 square metres and 12 panes into the calculator with 4mm clear float and ground floor access and you get roughly $1,400 to $2,900 for the lot, which is $120 to $240 a pane. That is well under the $180 to $450 single pane rate on our price list, and that is not a discount, it is what happens when twelve panes share one trip, one setup and one clean up.
Two adjustments to that number. The sidelight beside the front door needs Grade A safety glass under AS 1288, so price that one pane as toughened or laminated, which adds roughly $150 to $300 over the float rate for that single opening. And if the putty lines on the original sashes are cracked and falling out, which after ninety Hobart winters they usually are, tick the putty option and add $120 to $380 across the job. Final realistic band for the whole house: about $1,700 to $3,500.
The same house in low-E double glazed units is a different conversation. The glass and fit alone runs about $3,000 to $6,200 on those numbers, and old timber rebates almost always need deepening and new beads on top of that, which is where the $700 to $1,600 per window figure on the price list comes from. Our page on single versus double glazing is the honest comparison of what that buys you in a Hobart winter.
When you should not bother measuring, and what we will not do.
- If it is broken now, stop measuring and get it secured. A board up is $150 to $350 and we measure while we are there. Do not stand on a chair with a tape next to a cracked pane.
- If anything is toughened or made to order, your measurement will not be used anyway. Send rough numbers for the price and let the template do the real work.
- If the frame is rotten, the size of the glass is not your problem yet. Soft timber has to be repaired or the sash replaced first, and that is a carpenter or a joiner.
- We will not quote a firm price for toughened glass from a phone measurement, and you should be suspicious of anyone who does. It is not caution, it is that the glass cannot be fixed if the number is wrong.
- We do not do timber repairs, painting, plastering or new window frames. We measure, supply, cut, fit and seal glass, and we will tell you which trade has to come first.
Frequently asked questions
How many square metres of glass is a typical Hobart window?
Do I measure the old pane or the frame?
What thickness of glass do I need?
Can toughened glass be trimmed if I measure wrong?
Will a double glazed unit fit my old timber window?
Do I need to measure at all before getting a quote?
Send your sizes and get a real number
Send the pane sizes, the count and a photo of one corner with a tape in it, and we come back with a firm indicative price, usually the same business day.
Keep reading
- Hobart glass repair cost guide, what each job type costs.
- DIY versus professional replacement, what you can safely do yourself.
- AS 1288 safety glass compliance, which openings must be upgraded.
- Heritage sash reglazing, if the sashes are original.
- What happens on installation day, once the sizes are settled.
- Budget glass splashbacks and the 2026 price list.