The fuel tank as a measuring jug
Saws are designed so a tank of oil lasts about as long as a tank of fuel, which is quietly useful: it means you already own the equipment to measure oiler output. Fill both, cut until the fuel runs out, and look at the oil. With the defaults in the form — a 0.5 L fuel tank, a 0.26 L oil tank, 20 percent of the oil still there after 25 minutes — the saw used 208 mL of bar oil on one tank of fuel, which is 8.32 mL a minute or 499 mL an hour of cutting.
That is a figure for your saw with your bar on the wood you were in, which is worth more than any published number, because published numbers cannot know any of those things.
Reading it as a ratio, and the convention that trips people
208 mL of oil against 500 mL of fuel is 0.416 parts oil to one part fuel, or 2.40 parts fuel to one part oil. It is worth being explicit about which way round a ratio is written, because the mixing side of the same saw uses the opposite convention and catches people out: a 50 to 1 premix means 50 parts petrol to 1 part oil, so the oil is one part in 51 of the finished can — 1.96 percent of it, not 2.00 percent.
Bar oil never gets mixed with anything, so the share-of-total reading is only there for comparison. The two liquids live in separate tanks and do entirely separate jobs.
What a season costs
At 499 mL an hour, forty hours of cutting takes 19.9 litres of bar oil, which is 5.27 US gallons and therefore six one-gallon containers with about three litres left over. At 16 dollars a container the oil actually used is worth 84.30 dollars, or 2.11 dollars per cutting hour.
Against that, the same forty hours burns 1,200 mL an hour of mixed fuel — 12.7 US gallons — which at 5.50 dollars a gallon is 69.80 dollars. Bar oil is the larger of the two bills, at 55 percent of what goes into the saw by cost, and almost nobody expects that. The oil is quietly the expensive part.
Why the number moves
Oiler output tracks chain speed, so a saw that spends a tank at working revs pumps considerably more than one that idles between cuts. Many saws have an adjustable pump, which shifts it again. A longer bar has more rail to keep wet and takes more oil to do it, and hardwood in summer takes more than softwood in winter. All of that means the figure is a snapshot of the conditions it was measured in, and re-measuring after changing a bar is worth the tank it costs.
Measuring it better
Reading a level in a sight window to the nearest ten percent is the weak link, and the arithmetic can only be as good as it. Two ways to tighten it: weigh the whole saw before and after the tank on a kitchen scale, which turns the oil into grams and removes the eyeballing entirely, or simply run the test three times and take the average. Either is a large improvement on a single glance at a tank, and both take less time than looking the number up and finding out it depends on things nobody stated.
Questions people ask
How much bar oil does a chainsaw use?
For the saw in the form — 0.5 L of fuel, 0.26 L of oil, 20 percent of the oil left after a 25 minute tank — it is 208 mL per tank of fuel, or 8.3 mL a minute and 499 mL an hour of cutting. Yours will differ with bar length, pump setting, how hard the saw is worked and what it is cutting, which is why measuring your own tank beats looking a number up.
Should a chainsaw use a tank of bar oil per tank of fuel?
Saws are generally built so the two land close together, and the page prints what oiler output would empty your oil tank in exactly one fuel tank so you can compare. What it will not do is tell you whether your saw is behaving correctly — an oiler that is not delivering is a matter for the saw and its documentation, not for arithmetic.
Is bar oil the same as two stroke mix oil?
No. Mix oil goes into the petrol at the ratio your manual specifies and passes through the engine. Bar oil sits in its own tank and is pumped onto the chain and the bar rails; it never reaches the combustion chamber. They are separate products, bought separately and counted separately, and this page counts only the second.
Does bar oil cost more than fuel?
On the figures in the form it does — 84.30 dollars of oil against 69.80 dollars of mixed fuel over forty cutting hours, so oil is 55 percent of what goes into the saw by cost. That surprises most people. It depends entirely on your prices and your oiler setting, and the page recalculates it from whatever you enter.
How do I measure my chainsaw oiler output?
The rough way is to fill both tanks, cut until the fuel runs out, and read the oil level. The better way is to weigh the saw before and after on a kitchen scale, which converts the oil straight into grams and takes the eyeballing out. Timing a minute of output at working speed into a container works too, and the page accepts that directly.