The big picture:

I read these spec tables as work-cycle claims dressed up as physical numbers.

Nothing on that page is a field test. The machine reaches its top mark only if it can run most of the day, and the same table shows how much of the day it spends charging instead. On the 420 iQ it cuts for 84 minutes and charges for 54, which puts 60.9% of its own clock into mowing [1]. A robot that recharges every hour and a half spreads a full cut across the daylight, not across one afternoon.

Navimow makes the same admission on a different basis. Its sizing guide gives mowing area per charge beside a recommended lawn size: 265 square metres per charge on the i208 LiDAR, a model it sells for lawns of 800 to 2,000 square metres [3]. That is a three-fold gap at the bottom of the band and 7.5-fold at the top, and a buyer collects the bigger number only if the machine works through several charge cycles in a day.

The price ladder runs the opposite way, and that is where the money hides. Kress lists a quarter-acre machine at $2,799.98 and a seven-acre machine at $15,699.98, which is $11,199.92 against $2,242.85 per rated acre [4]. The step from a quarter-acre rating to a one-and-a-quarter-acre rating costs $1,400, so the smallest tier is the one that costs most per acre of rating.

The slope column carries its own split, and the small number sits deep in the table. Husqvarna rates the 420 iQ for a 15% maximum slope at the boundary and 45% inside the mowing area [1]. The all-wheel-drive 435 iQ prints 50% at the boundary against 70% inside [2]. The help answer on the same page quotes only the inside figure, describing “steep slopes of up to 45% (approximately 24 degrees) inside the boundary area” and leaving the boundary line out of the sentence [1].

By the numbers

  • 0.4 acres — Derated capacity: A one-acre rating at the floor of the ±20% band, times the irregular-mowing column, leaves 0.40 acres of usable space on a cluttered lot [1].
  • 15% — Boundary slope: The 420 iQ handles a 15% maximum slope at the boundary, against 45% inside the mowing area, in the same row of the table [1].
  • $8,249.97 — Cost per usable acre: The $3,299.99 price divided by 0.40 usable acres, against $3,299.99 per systematic acre [1].
  • $11,199.92 to $2,242.85 — Price per rated acre: Kress’s quarter-acre tier against its seven-acre tier, a five-fold spread across one brand’s ladder [4].

What I’d watch:

My eye goes to the place where a brand’s own help answer fights its own spec line. The 435 iQ table claims 1.3 acres with a ±20% tolerance, and the help answer on the same page says the machine handles rough ground up to 0.9 acres [2]. Both numbers belong to the vendor, and that gap is where sizing rows start with a dealer.

  • Where the wear clock runs: Blade sets are rated at 500 to 1,000 mowing hours per set, rather than in months [1]. A machine that cuts 60% of the day burns through that time faster than its owner expects, because the hour meter runs while the calendar does not.
  • What a dated sale hides: Kress’s marked-down rows carry a printed end date of December 31, 2026, or while supplies last [4]. A lasting choice should ride on the list price, since the sale row will vanish quickly.
  • Where the slope number comes from: On the Navimow line the same terrace moves from 45% to 55% to 84% as the model tier rises [3]. When a number acts like an upgrade, my read is that it works as a product perk rather than a baseline trait of the class.

The catch

The honest limit is that every figure here is a maker’s claim. No page I could reach prints a timed run over a real lot or an outside slope test.

On a clean rectangular lawn the systematic column is the fair one, and the one-acre rating holds up well enough that the double derating looks harsh. The ±20% band cuts both ways too: at the top of it the same machine is a 1.2-acre machine on a tidy lot, and the band never says which end a given yard lands on.

The boundary slope figure needs its own caveat. The table prints it without saying which task it governs, whether it limits where the boundary can be drawn or how the machine crosses the line. The 420 iQ is a wire-free unit, so there is no buried wire for the figure to describe [1]. I am not going to invent a mechanism the page does not state. What I can say is that the number is a third of the headline slope on the 420 iQ and 20 points lower on the 435 iQ, and a lot whose boundary crosses a bank is where that gap bites.

The habit repeats across this desk’s work on best-case numbers, including the window whose published efficiency gain turned out to be a best case rather than an average.

At a glance

  • The Big Shift: Robotic mowers sell on a headline acreage, while the same spec sheet buries a ±20% tolerance and an irregular-mowing figure at half the headline, so the printed number is a best case rather than a capacity.
  • Why It Matters: The derating rewrites the price. A $3,299.99 machine rated at one acre is $8,249.97 per usable acre on a cluttered lot, and the small rungs of a price ladder can run five times dearer per rated acre than the large ones.
  • What I’d Watch:
  • The brand’s own answers: Help pages that quote a smaller area than the spec line, as the 435 iQ does at 0.9 against 1.3 acres.
  • The boundary column: The lower of the two printed slope figures, which sits at a third of the headline on the 420 iQ and which the page never explains.
  • The work cycle: The split of cutting time against charging time, which decides how much of a day a full pass really takes.
  • The Catch: Every figure is a maker’s claim with no outside test behind it, and the tolerance band means a tidy, simple lawn can still reach close to the headline acreage.

Sources

[1] Husqvarna, “Automower® 420 iQ” product page and spec table — https://www.husqvarna.com/us/robotic-lawn-mowers/automower-420-iq/ [2] Husqvarna, “Automower® 435 iQ AWD” product page and spec table — https://www.husqvarna.com/us/robotic-lawn-mowers/automower-435-iq-awd/ [3] Segway, “Navimow” robotic mower range and sizing guide — https://navimow.segway.com/ [4] Kress, “Robotic lawn mowers” range and price list — https://www.kress.com/en-us/robotic-mowers