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Snow Weight Calculator — What the Snow on a Roof Weighs

What the snow on a roof weighs, from its depth and the kind of snow, per area and in all: a figure for information, never a design snow load.

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How deep the snow lies on the roof, measured straight down, averaged over the roof.

Push a rule or a marked pole straight down through the snow to the roof at several points you can reach safely from a ladder or a window, and average them. Measure at a level part of the roof, away from drifts against walls and parapets, which hold far more.

Tools needed: Rule or marked pole

How heavy the snow is for its depth: new snow is light, old settled snow several times heavier.

The figures are the National Building Code of Canada 2020's. New snow averages about 1 kN/m³ (6.4 pcf). As it settles it gets heavier: the code gives 2 to 5 kN/m³ (12.7 to 31.8 pcf) for old snow, seasonal snowpacks averaging about 2 kN/m³ (12.7 pcf) east of the Rockies and up to 4.21 kN/m³ (26.8 pcf) west of them, and an average of about 3 kN/m³ (19.1 pcf) measured in snow on roofs. Where you can, weigh a sample and use your own figure.

The roof's footprint seen from above: its length times its width, not the sloped surface.

Snow falls on the roof's plan, so measure the building's footprint including the overhangs, not along the slope. For a roof with several planes at different heights, run each separately; snow lies differently on each.

Tools needed: Tape measure, Building plans

Snow weight per area of roof

31.8 psf

Medium confidence

This is the weight of the snow on the roof at the depth and specific weight entered, for information only; it is not a design snow load and is compared with nothing. A roof's design load comes from the building code's ground snow load for the site and its factors for the roof: ASCE 7 for the US, the National Building Code for Canada, Eurocode 1 for the UK and Europe. The specific weight of snow varies widely with its age and wetness, which is why the figure is marked medium.

Snow on the whole roof, by mass
17.19 tons
The same weight as a depth of water
6.12 in
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • National Research Council of Canada, National Building Code of Canada 2020, Division B, Appendix C, Climatic and Seismic Information, Snow Loads: "The specific weight of old snow generally ranges from 2 to 5 kN/m3, and it is usually assumed in Canada that 1 kN/m3 is the average for new snow"; the seasonal snowpack averages 2.01 kN/m3 east of the continental divide (2.94 kN/m3 north of the treeline) and ranges from 2.55 to 4.21 kN/m3 west of it
  • National Building Code of Canada 2020, Note A-9.4.2.1.(1): values of the specific weight of snow on roofs measured at weather stations across Canada ranged from about 1.0 to 4.5 kN/m3, with an average of approximately 3.0 kN/m3; Article 4.1.6.13 takes the specific weight of snow in drifts as 4.0 kN/m3 or 0.43 Ss + 2.2 kN/m3, whichever is lesser, for design

Inputs used

Snow Depth on the Roof
20 in
What Kind of Snow
Snow on roofs, measured average — about 3.0 kN/m³ (19.1 pcf)
Specific Weight of Your Snow
19.1 pcf
Roof Plan Area
1080 sq ft

Intermediate steps

Snow on the whole roof, by mass
17.19 tons
The same weight as a depth of water
6.12 in
Final result31.83 psf

Confidence note: This is the weight of the snow on the roof at the depth and specific weight entered, for information only; it is not a design snow load and is compared with nothing. A roof's design load comes from the building code's ground snow load for the site and its factors for the roof: ASCE 7 for the US, the National Building Code for Canada, Eurocode 1 for the UK and Europe. The specific weight of snow varies widely with its age and wetness, which is why the figure is marked medium.

What this calculation does not cover

  • This is the weight of the snow at the depth and specific weight entered, for information. It is not a design snow load and says nothing about whether a roof can carry it: the design load comes from the building code's ground snow load for the site and its factors for the roof, ASCE 7 for the US, the National Building Code for Canada and Eurocode 1 (EN 1991-1-3) for the UK and Europe, and only the roof's design compares with that.
  • Snow does not lie evenly. It drifts against parapets, roof steps and rooftop units, slides off a steep upper roof onto the one below, and builds deeper in valleys, so a roof can carry several times the average in one place; one depth over the whole area misses all of it.
  • The specific weight changes as the snow lies: the National Building Code of Canada gives about 1 kN/m³ (6.4 pcf) for new snow and 2 to 5 kN/m³ (12.7 to 31.8 pcf) for old snow, and rain falling on snow adds water the depth does not show. A bucket of known volume and a scale give your own snow's figure directly.
  • The area is the roof's plan area, the horizontal footprint the snow falls on, not the sloped surface: on a pitched roof the sloped area is larger and would count the same snow twice.
  • Clearing snow from a roof is dangerous work; this page has nothing to say about whether, when or how to do it.

Add the equipment this sizes

This result is a specification — 31.8 psf — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-10-05 · v1.0.0

Regulatory standards & verification citations2
  1. National Research Council of Canada, National Building Code of Canada 2020, Division B, Appendix C, Climatic and Seismic Information, Snow Loads: "The specific weight of old snow generally ranges from 2 to 5 kN/m3, and it is usually assumed in Canada that 1 kN/m3 is the average for new snow"; the seasonal snowpack averages 2.01 kN/m3 east of the continental divide (2.94 kN/m3 north of the treeline) and ranges from 2.55 to 4.21 kN/m3 west of it
  2. National Building Code of Canada 2020, Note A-9.4.2.1.(1): values of the specific weight of snow on roofs measured at weather stations across Canada ranged from about 1.0 to 4.5 kN/m3, with an average of approximately 3.0 kN/m3; Article 4.1.6.13 takes the specific weight of snow in drifts as 4.0 kN/m3 or 0.43 Ss + 2.2 kN/m3, whichever is lesser, for design
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Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for.

How to calculate snow weight — what the snow on a roof weighs in 5 steps

  1. Snow Depth on the RoofHow deep the snow lies on the roof, measured straight down, averaged over the roof.
  2. What Kind of SnowHow heavy the snow is for its depth: new snow is light, old settled snow several times heavier.
  3. Specific Weight of Your SnowThe weight of a known volume of your snow, divided by that volume: 3.0 kN/m³ (19.1 pcf) opens.
  4. Roof Plan AreaThe roof's footprint seen from above: its length times its width, not the sloped surface.
  5. Snow weight per area of roofThe tool computes the snow weight per area of roof from those figures and shows the formula, its sources, and a confidence rating alongside it.

Snow weight per area of roof by snow depth on the roof

Page defaults, not your figures above.

Snow Depth on the RoofSnow weight per area of roof (psf)
10 in15.9
15 in23.9
20 in31.8
25 in39.8
30 in47.7
35 in55.7

Frequently asked questions

How much does a foot of snow on a roof weigh?
It depends on the snow far more than on the foot. At the National Building Code of Canada's 1 kN/m³ (6.4 pcf) for new snow, a foot (305 mm) of it weighs about 6.4 lb on every square foot (0.30 kN/m²); at the code's average for snow measured on roofs, about 3 kN/m³ (19.1 pcf), the same foot weighs about 19 lb a square foot (0.91 kN/m²); old snow at the heavy end of the code's range, 5 kN/m³ (31.8 pcf), is about 32 lb a square foot (1.52 kN/m²). Five times as much for the same depth.
Is this the snow load my roof is designed for?
No. This is what the snow on it weighs today. A roof's design snow load comes from the building code: the ground snow load for the site, from ASCE 7's maps in the US, the National Building Code's tables in Canada or Eurocode 1 and its national annex in the UK and Europe, turned into a roof load with factors for exposure, heat loss, roof shape, drifting and sliding snow. The ground-to-roof snow load page works the US design figure; comparing a weight with a design is a structural engineer's job, not this page's.
Why is old snow heavier than new snow?
Because it settles. New snow is mostly air, and as it lies it compacts under its own weight and partly melts and refreezes, so the same snow takes up less depth. Settling adds no weight: snow that sinks from 300 mm (11.8 in) at 1 kN/m³ (6.4 pcf) to 100 mm (3.9 in) at 3 kN/m³ (19.1 pcf) weighs 0.3 kN/m² (6.3 psf) before and after. What is heavier is a given depth: a depth of settled snow weighs more than the same depth of fresh snow, and the weight on the roof rises only when more snow or rain is added. The National Building Code of Canada gives about 1 kN/m³ (6.4 pcf) for new snow against 2 to 5 kN/m³ (12.7 to 31.8 pcf) for old.
How do I measure the weight of my own snow?
Weigh a sample. Push a bucket of known volume down through the snow, level it, and weigh it less the bucket; the weight over the volume is the snow's specific weight. Ten litres (2.64 US gallons) weighing 3 kg (6.6 lb) is about 2.94 kN/m³ (18.7 pcf). Take samples from several places, since the snow near the surface is lighter than the snow lower down.
Why does the page show the weight as a depth of water?
Because it is the easiest way to picture it: 1.5 kN/m² (31.3 psf) is the same weight as 153 mm (6 in) of water standing on the roof. Water weighs about 9.8 kN/m³ (62.4 pcf), so any snow load divided by that is the depth of water that would weigh the same.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.