about this leveler
A spirit level, built as a web page.
LevelerPro is a bubble leveler, a spirit level built as a web page. Four green vials sit on the top, right, bottom, and left edges of your screen, with a bullseye in the middle, and all five read live from your device’s tilt sensor. Set a phone or tablet flat on a surface and the bubble drifts toward the raised edge exactly as it would in a glass vial. There is nothing to download, no account to create, and no reading ever leaves the device.
What this leveler tool measures
The leveler reads gravity through the accelerometer already in your phone and turns it into two numbers: tilt left-to-right and tilt top-to-bottom. You can show those in degrees, percent slope, millimetres per metre, or inches per foot, so drainage falls and ramp gradients read straight off the screen without arithmetic. Three vial ranges cover different work: ±2° for cabinetry and shelving where a tenth of a degree matters, ±6° for general levelling, and ±15° for roughing in a slope. Set Zero cancels the small bias every sensor ships with, and Hold freezes a reading when the screen is somewhere you cannot see it.
Guides for the jobs people use it for
Reading a bubble is the easy part. These work through particular jobs end to end, including the tolerances that actually apply and the mistakes that cost the most time.
Levelling a washing machine
Appliances
Level a washing machine with a phone: which foot to turn, why diagonal rock matters more than tilt, and the tolerance that stops it walking on spin.
Fridges, dishwashers and cookers
Appliances
Why a fridge wants a deliberate backward tilt, why a dishwasher wants none, and how to level a freestanding cooker so pans do not slide.
Hanging a shelf level
Building & DIY
Level the bracket line rather than the board, and use the single-datum trick that keeps a run of shelves straight in a room where nothing is level.
Checking a floor before flooring
Building & DIY
Level and flat are different faults with different fixes. Survey a subfloor with a phone and a straightedge, then read it against flooring tolerances.
Slope and gradient conversion
Reference
Convert between degrees, percent slope, millimetres per metre, inches per foot and 1-in-N ratios, with the falls specified for common building jobs.
Levelling a camera tripod
Outdoors & travel
Level the tripod base, not the camera, and learn why a panorama needs it. Covers ball heads, levelling bases, bowl mounts and the pan test.
Levelling a caravan or RV
Outdoors & travel
Level side-to-side with ramps before you unhitch, then front-to-back on the jockey wheel. Includes the tolerance an absorption fridge really needs.
How to use it
Lay the device flat on the surface with its long edge along the run you care about, and give it a second to settle. Rest it on a reference you already trust and tap Set Zero, which removes your hardware’s built-in offset. Then read the raised edge: the bubble climbs toward the high side, and the vial gains a green halo once the surface is inside ±0.2°. For anything that matters, take the reading twice. Note it, turn the device end-for-end in the same spot, and read again. A true surface gives the same answer both ways, and the difference between them is your instrument’s error. The levelling guide works through calibration, vial placement, and the common jobs in detail.
Accuracy and limits
A calibrated phone is a good ±0.2° to ±0.5° instrument. That is enough for shelves, worktops, appliances, tripods, and fence rails. It is not enough for machine setup or anything specified in arc-minutes, where a ground machinist’s level earns its price. A phone also only sees the few centimetres beneath it, so on a wavy floor rest it on a straightedge and level that instead. The accuracy notes explain what the sensor can and cannot resolve, and why temperature moves the reading.
If you meant a different kind of leveler
The word covers several unrelated products, and this site is only the measuring instrument. A floor or self leveler is a pourable compound that flattens a slab; a dock leveler is the steel bridge plate at a loading bay; a cake leveler is a wire for trimming a sponge. We do not sell or document any of those, and you will be better served by the manufacturer’s data sheet. What this tool can do for those jobs is measure them: the fall on a dock apron in mm/m, or the high spot on a slab before you work out how deep a pour needs to be, which is covered in checking a floor is level and flat.
Leveler questions, answered.
Reading a bubble, using a phone as a level, calibration, and how close to level any given job actually needs to be.
What is a leveler?
A leveler is a tool that tells you whether a surface is horizontal. The classic form is a spirit level: a sealed glass vial of liquid with one air bubble that climbs to the highest point of the tube, so the bubble’s position reports the tilt. LevelerPro is the same instrument built as a web page, reading your device’s tilt sensor instead of a vial of spirit. The word is also used for unrelated products that flatten things rather than measure them, such as floor compounds and loading-dock plates.
How do you read a level bubble?
Put the level on the surface and look at the two lines etched in the middle of the vial, called the gate. If the bubble sits evenly between them, that axis is level. If it drifts to one side, that side is the high side, because the bubble always climbs toward the raised end, because air is lighter than the liquid around it. Shim the low end until the bubble centres. For a reading you can trust, note it, turn the level end-for-end in the same spot, and read again: a true surface gives the same answer both ways.
Can I use my phone as a leveler?
Yes. Every modern phone contains an accelerometer that measures the direction of gravity, which is the same physical quantity a spirit vial responds to. Lay the phone flat, screen up, and it can resolve tilt to roughly a tenth of a degree. Two cautions: the sensor ships with a small fixed bias, so calibrate it once on a surface you trust, and phone cases with raised lips or camera bumps will rock the device and spoil the reading. Take the case off for anything precise.
How do I check level online?
Open a browser-based level such as this page, with no install and no account. On a laptop or desktop there is no tilt sensor to read, so the tool falls back to a drag preview you can use to see how the vials behave; the live reading needs a device that actually has an accelerometer. Because the maths runs locally in JavaScript, the page works without a network round-trip once loaded, and no measurement is ever sent anywhere.
How do I check level by mobile?
Open levelerpro.com on the phone, then rest the phone flat on the surface. On iPhone, tap Enable Motion Sensor and allow Motion & Orientation access when Safari asks. iOS only grants it after a tap, and only over HTTPS. Android grants it automatically. Tap Set Zero while the phone sits on a reference surface, then read the vial on the edge that runs along whatever you are checking. Add the page to your home screen if you want it to open like an app.
What is the best free leveling app?
Judge one on four things rather than star ratings: can you calibrate it and clear that calibration; does it show real units such as degrees, percent slope and mm per metre; is it honest about accuracy instead of claiming a hundredth of a degree from a phone sensor; and does it work without demanding an account or your location. LevelerPro is free and needs no install, but the same checklist applies to any option, including the level built into iOS Measure.
How level is level enough?
It depends entirely on the job, and most people aim far tighter than they need to. A washing machine is within spec at 1°. A shelf looks right at anything under 0.5°, which is about 9 mm of fall per metre. A caravan needs about 3° for its fridge to work. A drainage run is the opposite problem: it must slope, typically 1:80 or 12.5 mm per metre. Chasing hundredths of a degree is wasted effort, because a phone is honestly a ±0.2° to ±0.5° instrument once calibrated.
Do I need to calibrate a phone level?
Once, yes. Every accelerometer leaves the factory with a small fixed bias, often a few tenths of a degree and sometimes over a full degree, and no amount of careful measuring will remove it. Rest the device on a surface you already trust, tap Set Zero, and that offset is subtracted from every later reading and stored on the device. Recalibrate after a big temperature change, after dropping the phone, or any time the resting reading looks wrong.
Does an online level work without internet?
After the first load, yes. The page is static and all the maths runs locally in JavaScript, so there is no server call behind a reading. Once the page is open it keeps working with the connection off, which matters in a loft, a basement, or on a pitch with no signal. Add it to your home screen and it opens like an app.
Which units should I use?
Degrees for anything you are levelling flat, because tolerances for shelves and appliances are quoted that way. Millimetres per metre for anything you are deliberately sloping, since drainage and ramp specs are written as falls and the number then reads straight off the screen with no arithmetic. Percent slope for ramps and paths, and inches per foot if you are working from North American plumbing figures. The conversion table covers all four.